Trane and American Standard furnace codes (LED flashes and error codes)

77 codes for 42 model series, each with the wording and source from Trane installation, operation and maintenance documents.

How House Works EditorialChecked against 52 sources, October 2026

Prepared by: How House Works Editorial
How it is checked: Methodology
Sources: 52 documents, listed at the end
Page: HHW · ERROR-CODES · TRANE
Based on: Trane installation, operation and maintenance documents

Meanings are quoted from Trane installation, operation and maintenance documents. The "Who" column is our reading of the remedy in those documents: whether an owner can do the first checks, or the fix belongs to a licensed technician.

Codes with step-by-step checks

2 flashesSystem lockout
3 flashesDraft or pressure switch
4 flashesLimit or rollout open
6 flashesPolarity, ground or igniter
9 flashesIgniter relay or inducer limit
E2.1Retries exceeded, lockout
E3.1Shorted pressure switch
E04Open limit
E11Internal gas valve error
E12Open fuse

How it works: How a gas furnace lights, and how the control board blinks a failure code

Code	Meaning	Who	Series	Source
1 flash	“NORMAL OPERATION - Flash every 20 seconds”	Owner can check	12 series UH1, DH1, UD1, DD1, UX2, DX2, UD2, DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	18-CH93D1-1A-EN p. 2; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CH92D1-1A-EN p. 2
2 flashes	“System Lockout (Retries or Recycles exceeded)” What to check	Owner checks, then technician	21 series UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UX2, DX2, UD2, UD1-H, DD1-H, UE1, *DE1, CUX1, CDX1, CUB1, CDB1	12 documents 18-CD29D1-18-EN p. 40; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
2 flashes	“Flame lost or Ignition failure” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
2 flashes	“Soft lockout due to flame lost or ignition retries” What to check	Owner checks, then technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
2 flashes	“External lockout (retries or recycles exceeded)” What to check	Owner checks, then technician	(board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	18-CH42D1-2 p. 6; 18-CH46D1-2 p. 6; 18-CH50D1-2 p. 7
2 flashes	“RETRIES OR RECYCLES EXCEEDED” What to check	Technician	UH2, DH2	18-CD26D1-23-EN p. 44
2 flashes	“SYSTEM LOCKOUT RETRIES OR RECYCLES EXCEEDED” What to check	Owner checks, then technician	12 series UH1, DH1, UD1, DD1, UX2, DX2, UD2, DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	18-CH93D1-1A-EN p. 2; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CH92D1-1A-EN p. 2
3 flashes	“Draft Pressure Error - Possible problems: a) Venting problem b) Pressure switch problem c) Inducer problem” What to check	Technician	17 series UH1-H, DH1-H, UC1, DC1, UX1, DX1, UX2, DX2, UD2, UD1-H, DD1-H, UE1, *DE1, CUX1, CDX1, CUB1, CDB1	10 documents 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
3 flashes	“Pressure Switch Failure” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
3 flashes	“Pressure switch/Inducer error” What to check	Technician	(board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	18-CH42D1-2 p. 6; 18-CH46D1-2 p. 6; 18-CH50D1-2 p. 7
3 flashes	“Draft Pressure Error - Possible problems a) Venting problem b) Pressure seitch problem c) Inducer problem” What to check	Technician	UD1, DD1	18-CD19D7-29-EN p. 22
3 flashes	“Draft Pressure Error - Possible problems a) Venting problem b) Pressure switch problem c) Inducer problem” What to check	Technician	UH1, DH1	18-CD29D1-18-EN p. 40
3 flashes	“INDUCER OR PRESSURE SWITCH ERROR” What to check	Technician	UH2, DH2	18-CD26D1-23-EN p. 44
3 flashes	“PRESSURE SWITCH FAULT” What to check	Technician	12 series UH1, DH1, UD1, DD1, UX2, DX2, UD2, DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	18-CH93D1-1A-EN p. 2; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CH92D1-1A-EN p. 2
4 flashes	“Open Temperature Limit Circuit” What to check	Technician	16 series UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1	8 documents 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
4 flashes	“High Temp Limit Fault” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
4 flashes	“Roll Out Fault” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
4 flashes	“Open Temperature Limit Switch” What to check	Technician	UX2, DX2, *UD2	18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28
4 flashes	“Open limit switch & Aux & Rollout” What to check	Technician	(board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	18-CH42D1-2 p. 6; 18-CH46D1-2 p. 6; 18-CH50D1-2 p. 7
4 flashes	“Open High Limit Device” What to check	Technician	UH1, DH1	18-CD29D1-18-EN p. 40
4 flashes	“OPEN LIMIT OR ROLLOUT SWITCH” What to check	Technician	UH2, DH2	18-CD26D1-23-EN p. 44
4 flashes	“OPEN LIMIT SWITCH” What to check	Technician	12 series UH1, DH1, UD1, DD1, UX2, DX2, UD2, DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	18-CH93D1-1A-EN p. 2; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CH92D1-1A-EN p. 2
5 flashes	“Flame sensed when no flame should be present”	Technician	31 series UH2, DH2, UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UX2, DX2, UD2, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed), DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	15 documents 18-CD26D1-23-EN p. 44; 18-CH93D1-1A-EN p. 2; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28; 18-CH42D1-2 p. 6; 18-CH46D1-2 p. 6; 18-CH50D1-2 p. 7; 18-CH92D1-1A-EN p. 2
5 flashes	“Flame Detect Fault”	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
6 flashes	“115 volt AC power reversed, poor grounding or system voltage too low” What to check	Technician	14 series UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1	7 documents 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
6 flashes	“Line Polarity Fault” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
6 flashes	“Ground Fault” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
6 flashes	“Ignition Means Fault” What to check	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
6 flashes	“115 volt AC power reversed, ignitor (Triac) fault, poor grounding or system voltage too low” What to check	Technician	UX2, DX2, *UD2	18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28
6 flashes	“115 Volt AC power reversed or Poor Grounding or system voltage too low” What to check	Technician	UD1, DD1	18-CD19D7-29-EN p. 22
6 flashes	“115 Volt AC power reversed or Poor Grounding” What to check	Technician	UH1, DH1	18-CD29D1-18-EN p. 40
6 flashes	“LINE REVERSE POLARITY” What to check	Technician	UH2, DH2	18-CD26D1-23-EN p. 44
6 flashes	“Reversed polarity, or Igniter (Triac) Fault” What to check	Technician	(board CNT04829; furnace models not listed), (board CNT05457; furnace models not listed)	18-CH42D1-2 p. 6; 18-CH50D1-2 p. 7
6 flashes	“Reversed polarity, or Igniter (Triac) Fault / Ground fault” What to check	Technician	(board CNT05141; furnace models not listed)	18-CH46D1-2 p. 6
6 flashes	“115 VOLT AC POWER REVERSED OR IMPROPER GROUND” What to check	Technician	10 series UH1, DH1, UD1, DD1, UX2, DX2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	18-CH93D1-1A-EN p. 2; 18-CH111D1-1A-EN p. 2; 18-CH92D1-1A-EN p. 2
6 flashes	“115 VOLT AC POWER REVERSED OR IGNITER FAULT” What to check	Technician	UD2, DD2	18-CH76D1-1A-EN p. 2
7 flashes	“Gas valve circuit error”	Technician	28 series UH2, DH2, UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UX2, DX2, UD2, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1, DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	12 documents 18-CD26D1-23-EN p. 44; 18-CH93D1-1A-EN p. 2; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28; 18-CH92D1-1A-EN p. 2
7 flashes	“Gas Valve Fault”	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
7 flashes	“External gas valve circuit error”	Technician	(board CNT04829; furnace models not listed), (board CNT05457; furnace models not listed)	18-CH42D1-2 p. 6; 18-CH50D1-2 p. 7
7 flashes	“External gas valve circuit error (voltage sensed when it should not be sensed)”	Technician	(board CNT05141; furnace models not listed)	18-CH46D1-2 p. 6
8 flashes	“Low flame sense signal”	Technician	26 series UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UX2, DX2, UD2, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1, DD2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	11 documents 18-CH93D1-1A-EN p. 2; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CH111D1-1A-EN p. 2; 18-CH76D1-1A-EN p. 2; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28; 18-CH92D1-1A-EN p. 2
8 flashes	“Low Flame Signal”	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
8 flashes	“Low flame sense”	Technician	6 series UX2, DX2, *UD2, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	6 documents 18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28; 18-CH42D1-2 p. 6; 18-CH46D1-2 p. 6; 18-CH50D1-2 p. 7
8 flashes	“WEAK FLAME”	Technician	UH2, DH2	18-CD26D1-23-EN p. 44
9 flashes	“Ignitor Relay Fault” What to check	Technician	6 series UH1, DH1, UC1, DC1, UD1, DD1	18-CD29D1-18-EN p. 40; 18-CD19D5-35-EN p. 40; 18-CD19D7-29-EN p. 22
9 flashes	“Open Inducer Limit switch” What to check	Technician	5 series UX2, DX2, *UD2, (board CNT04829; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28; 18-CH42D1-2 p. 6; 18-CH50D1-2 p. 7
9 flashes	“High Temp Limit Fault” What to check	Technician	5 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed)	18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7
9 flashes	“Check Ignitor Circuit and Line "N" to 24VAC "Common" voltage (≤ 2 volts) [possible grounding problem]” What to check	Technician	UX1, DX1, UD1-H, DD1-H	18-CD19D6-34 p. 39; 18-CD21D1-15-EN p. 24
9 flashes	“Check Ignitor Circuit and Line "N" to 24VAC "Common" voltage (< 2 volts) [possible grounding problem]” What to check	Technician	UH1-H, DH1-H	18-CD33D1-11-EN p. 39
9 flashes	“OPEN INDUCER LIMIT ERROR” What to check	Technician	UH2, DH2	18-CD26D1-23-EN p. 44
9 flashes	“IGNITER RELAY FAULT” What to check	Technician	10 series UH1, DH1, UD1, DD1, UX2, DX2, DD (1990-1999 families), DC (1990-1998 families), M951, *UX R-series (e.g. AUX060R936W3)	18-CH93D1-1A-EN p. 2; 18-CH111D1-1A-EN p. 2; 18-CH92D1-1A-EN p. 2
9 flashes	“OPEN INDUCER LIMIT” What to check	Technician	UD2, DD2	18-CH76D1-1A-EN p. 2
10 flashes	“Communication Fault”	Technician	9 series UHM, DHM, UH3, DH3, UD2, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed), DD2	6 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH76D1-1A-EN p. 2; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
10 flashes	“Communication Busy Fault”	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
10 flashes	“Communication Failure”	Technician	UHM, DHM, (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	18-CD30D1-21-EN p. 55; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
10 flashes	“Inducer communication error”	Technician	UX2, DX2, *UD2	18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28
10 flashes	“Communication Error”	Technician	(board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	18-CH42D1-2 p. 6; 18-CH46D1-2 p. 6; 18-CH50D1-2 p. 7
E01	“Loss of the IRQ or other internal failures (Internal IFC error)”	Technician	6 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58
E01	“Loss of the IRQ or other internal IFC failures”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E01	“Internal IFC failure”	Technician	L8V1	FNR-SVX007A-EN p. 43
E01	“Loss of the IRQ or other internal failures”	Technician	S9VM	FNR-SVX006B-EN p. 104
E1.0	“Loss of the IRQ or other internal failures”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E2.1	“Retry Exceeded (Flame never sensed, one hour lockout after 3 times)” What to check	Owner checks, then technician	6 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58
E2.1	“Retries exceeded (Flame never sensed, one hour lockout after 7 times)” What to check	Owner checks, then technician	S8V2-C	FNR-SVX003A-EN p. 59
E2.1	“Flame never sensed (5 retries, 6 total results in one hour lockout)” What to check	Owner checks, then technician	L8V1	FNR-SVX007A-EN p. 43
E2.1	“Retries Exceeded - 1 hour lockout” What to check	Owner checks, then technician	S9VM	FNR-SVX006B-EN p. 104
E2.1	“Retry exceeded” What to check	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E2.2	“Recycles Exceeded (Flame sensed then lost, one hour lockout after 10 times)”	Owner checks, then technician	7 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58; FNR-SVX003A-EN p. 59
E2.2	“Flame sensed and lost (9 recycles, 10 total results in one hour lockout)”	Owner checks, then technician	L8V1	FNR-SVX007A-EN p. 43
E2.2	“Recycles Exceeded - 1 hour lockout”	Owner checks, then technician	S9VM	FNR-SVX006B-EN p. 104
E2.2	“Recycles exceeded”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E2.3	“1st Stage Gas Valve Not Energized When It Should Be exceeded after 10 times”	Technician	7 series S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2	FNR-SVN001A-EN p. 45; FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58
E2.3	“1st stage gas valve not energized when it should be (10 times)”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E2.3	“First stage gas valve not energized when it should be”	Technician	L8V1	FNR-SVX007A-EN p. 43
E2.3	“1st Stage Gas Valve Not energized When It Should Be (After 10 Times)”	Technician	S9VM	FNR-SVX006B-EN p. 104
E2.4	“HLO relay not energized when it should be”	Technician	L8V1	FNR-SVX007A-EN p. 43
E2.4	“General Gas Valve Lockout”	Owner checks, then technician	S9VM	FNR-SVX006B-EN p. 104
E3.0	“Combustion Pressure Alert”	Technician	S9VM	FNR-SVX006B-EN p. 105
E3.1	“Shorted Pressure Switch, 1st Stage” What to check	Technician	9 series S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C, S9VM	5 documents FNR-SVN001A-EN p. 45; FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58; FNR-SVX003A-EN p. 59; FNR-SVX006B-EN p. 105
E3.1	“Shorted Pressure Switch” What to check	Technician	S8B1	18-CE09D1-1E-EN p. 54
E3.1	“Signal Not Present Less than 0.25VDC @ 5.0VDC supply for 2 secs. (RD - GND)” What to check	Technician	L8V1	FNR-SVX007A-EN p. 43
E3.2	“Open Pressure Switch, 1st Stage”	Technician	9 series S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C, S9VM	5 documents FNR-SVN001A-EN p. 45; FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58; FNR-SVX003A-EN p. 59; FNR-SVX006B-EN p. 105
E3.2	“Open Pressure Switch”	Technician	S8B1	18-CE09D1-1E-EN p. 54
E3.2	“Signal Out of Bounds Greater than 4.25V @ 5.0V supply for 10 secs. (RD - GND)”	Technician	L8V1	FNR-SVX007A-EN p. 43
E3.3	“Shorted Pressure Switch, 2nd Stage (S8X2 only)”	Technician	S8B1, S8X1, S8X2	18-CE14D1-1A-EN p. 58
E3.3	“Shorted Pressure Switch, 2nd Stage (Not Applicable for S8B1, S8X1)”	Technician	S8B1, S8X1, S8X2	S8XB-SVX001-1D-EN p. 58
E3.3	“Shorted Pressure Switch, 2nd Stage (Not applicable for S9X1/S9B1)”	Technician	S9X1, S9X2, S9B1	FNR-SVX002B-EN p. 98
E3.3	“Shorted pressure switch, 2nd stage”	Technician	S9V2-VC (Link kit), S8V2-C	FNR-SVN001A-EN p. 45; FNR-SVX003A-EN p. 59
E3.3	“Insufficient Pressure Inducer is unable to reach pressure setting at maximum speed after 10 seconds. (PI - GND)”	Technician	L8V1	FNR-SVX007A-EN p. 43
E3.4	“Open Pressure Switch, 2nd Stage (S8X2 only)”	Technician	S8B1, S8X1, S8X2	18-CE14D1-1A-EN p. 58
E3.4	“Open Pressure Switch, 2nd Stage (Not Applicable for S8B1, S8X1)”	Technician	S8B1, S8X1, S8X2	S8XB-SVX001-1D-EN p. 58
E3.4	“Open Pressure Switch, 2nd Stage (Not applicable for S9X1/S9B1)”	Technician	S9X1, S9X2, S9B1	FNR-SVX002B-EN p. 98
E3.4	“Open pressure switch, 2nd stage”	Technician	S9V2-VC (Link kit), S8V2-C	FNR-SVN001A-EN p. 45; FNR-SVX003A-EN p. 59
E3.5	“Combustion Pressure Low”	Technician	S9VM	FNR-SVX006B-EN p. 105
E3.5	“Open Pressure Switch, 2nd Stagewith 2nd Stage Gas Valve Energized without request”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E3.6	“Combustion Pressure High”	Technician	S9VM	FNR-SVX006B-EN p. 105
E3.7	“Combustion Transducer out of bounds too low or no output”	Technician	S9VM	FNR-SVX006B-EN p. 105
E3.8	“Combustion Transducer out of bounds too high”	Technician	S9VM	FNR-SVX006B-EN p. 105
E04	“Open Limit (Main Thermal, Rollout Switch, or Reverse Airflow Switch)” What to check	Technician	6 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58
E4.0	“Open High Limit”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 45; FNR-SVX006B-EN p. 105
E4.0	“Open high limit switch”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E04	“A thermal limit has opened in the safety circuit” What to check	Technician	L8V1	FNR-SVX007A-EN p. 43
E4.1	“Open Reverse Airflow Limit”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 45; FNR-SVX006B-EN p. 105
E4.1	“Open reverse air-flow limit switch”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E4.2	“Open Rollout Limit”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 45; FNR-SVX006B-EN p. 105
E4.2	“Open roll-out limit switch”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E05	“Flame detected, should not be present”	Technician	6 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58
E5.0	“Flame Detected, Should Not Be Present”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 45; FNR-SVX006B-EN p. 105
E05	“Flame detected when it should not be present”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E05	“Flame sensed when no flame should be present”	Technician	L8V1	FNR-SVX007A-EN p. 43
E6.1	“Voltage reversed polarity”	Technician	8 series S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C	FNR-SVN001A-EN p. 45; FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58; FNR-SVX003A-EN p. 59
E6.1	“Hot & neutral reversed”	Technician	L8V1	FNR-SVX007A-EN p. 43
E6.1	“Incoming High Voltage Reversed Polarity”	Technician	S9VM	FNR-SVX006B-EN p. 105
E6.2	“Bad grounding”	Technician	8 series S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C	FNR-SVN001A-EN p. 45; FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58; FNR-SVX003A-EN p. 59
E6.2	“Ground not detected”	Technician	L8V1	FNR-SVX007A-EN p. 43
E6.2	“Insufficient / Bad Grounding”	Technician	S9VM	FNR-SVX006B-EN p. 105
E6.3	“(1) Igniter relay fails (2) Igniter open”	Technician	6 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 59
E6.3	“(1) Igniter open or igniter relay failure on IFC (2) Igniter relay failure on IFC”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E6.3	“Igniter Relay Failure Igniter Open”	Technician	S9VM	FNR-SVX006B-EN p. 105
E6.3	“1. Igniter relay fails 2. Igniter open 3. Ignitor Lockout”	Owner checks, then technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E7.1	“1st stage gas valve (MVL) is energized when it should be off”	Technician	S8B1, S8X1, S8X2, L8V1	S8XB-SVX001-1D-EN p. 59; FNR-SVX007A-EN p. 43
E7.1	“1st Gas valve (MVL) is energized when it should be off”	Technician	S9X1, S9X2, S9B1	FNR-SVX002B-EN p. 98
E7.1	“Gas valve (MVL) is energized when it should be off”	Technician	S8B1	18-CE09D1-1E-EN p. 54
E7.1	“1st stage gas valve energized without request”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E7.1	“Gas Valve Energized Without Request”	Technician	S9VM	FNR-SVX006B-EN p. 105
E7.1	“Gas Valve Energized without Request, 1st Stage”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E7.2	“Redundant Relay (HLO output) Energized when it should be Off”	Technician	S9V2-VC (Link kit), L8V1, S9VM	FNR-SVN001A-EN p. 45; FNR-SVX007A-EN p. 43; FNR-SVX006B-EN p. 105
E7.2	“Redundant relay (HLO output) energized when it should not be”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E08	“Flame current is low, but still strong enough to allow operation”	Technician	7 series S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, L8V1	FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 59; FNR-SVX007A-EN p. 43
E08	“Low flame sense. Current is low but strong enough for operation”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E8.0	“Flame Current Is Low, But Strong Enough For Operation”	Technician	S9VM	FNR-SVX006B-EN p. 106
E8.0	“Flame current is low, but still strong enough to allow operation.”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E8.1	“Retry, No Flame Detected”	Technician	S9VM	FNR-SVX006B-EN p. 106
E8.2	“Recycle, Unexpected Flame Loss”	Technician	S9VM	FNR-SVX006B-EN p. 106
E09	“Open Inducer Limit Switch or Condensate Pressure Switch”	Technician	S9X1, S9X2, S9B1	FNR-SVX002B-EN p. 98
E9.1	“Open Inducer Limit Switch”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 45; FNR-SVX006B-EN p. 106
E9.2	“Open Condensate Switch”	Technician	S9VM	FNR-SVX006B-EN p. 106
E9.2	“Open Condensate Pressure Switch”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 45
E9.3	“Condensate Lockout”	Owner checks, then technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 45; FNR-SVX006B-EN p. 106
E9.4	“24V detected on CSI or ILI when it should not be present (S8V2- PC control installed in S9V2-VC furnace)”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E10	“Inducer motor no communication response”	Technician	L8V1	FNR-SVX007A-EN p. 43
E10.1	“Communication is lost between the VSDI Motor Control and the furnace control”	Technician	S9VM	FNR-SVX006B-EN p. 106
E10.1	“Communication is lost between the VSIM Motor Control and the furnace control”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E10.2	“The variable speed inducer has reached its maximum speed limit.”	Technician	S9VM	FNR-SVX006B-EN p. 106
E10.3	“The variable speed inducer has reached its minimum speed limit.”	Technician	S9VM	FNR-SVX006B-EN p. 106
E10.4	“The variable speed inducer control board or inducer motor has failed.”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 46; FNR-SVX006B-EN p. 106
E11	“(1) 1st stage gas valve not energized when it should be (2) 1st stage gas valve relay stuck closed (3) 2nd stage gas valve relay stuck closed (S8X2 only) (4) 2nd stage gas valve energized when it should not be (S8X2 only) (5) 2nd stage gas valve not energized when it should be (S8X2 only)” What to check	Technician	S8B1, S8X1, S8X2	18-CE14D1-1A-EN p. 58
E11	“(1) 1st stage gas valve not energized when it should be (2) 1st stage gas valve relay stuck closed (3) 2nd stage gas valve relay stuck closed (Not Applicable for S8B1, S8X1) (4) 2nd stage gas valve energized when it should not be (Not Applicable for S8B1, S8X1) (5) 2nd stage gas valve not energized when it should be (Not Applicable for S8B1, S8X1)” What to check	Technician	S8B1, S8X1, S8X2	S8XB-SVX001-1D-EN p. 59
E11	“(1) 1st stage gas valve not energized when it should be (2) 1st stage gas valve relay stuck closed (3) 2nd stage gas valve relay stuck closed (Not applicable for S9X1/S9B1) (4) 2nd stage gas valve energized when it should not be (Not applicable for S9X1/S9B1) (5) 2nd stage gas valve not energized when it should be (Not applicable for S9X1/S9B1)” What to check	Technician	S9X1, S9X2, S9B1	FNR-SVX002B-EN p. 98
E11	“(1) 1st stage gas valve not energized when it should be (2) 1st stage gas valve relay stuck closed (3) 2nd stage gas valve relay stuck closed (4) 2nd stage gas valve energized when it should not be (5) 2nd stage gas valve not energized when it should be” What to check	Technician	S8X1, S8X2	18-CE04D1-1D-EN p. 58
E11	“Gas valve not energized when it should be Gas valve relay stuck closed” What to check	Technician	S8B1	18-CE09D1-1E-EN p. 54
E11	“(1) 1st stage gas valve not energized when it should be (2) 2nd stage gas valve energized without request (3) 2nd stage gas valve not energized when it should be (4) Gas valve relay stuck closed” What to check	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E11	“1st stage gas valve energized when it should not be 1st stage gas valve not energized when it should be Redundant relay (HLO output) not energized when it should be. After 10 unsuccessful tries, E11 will populate and enter into a one hour lockout” What to check	Owner checks, then technician	L8V1	FNR-SVX007A-EN p. 43
E11	“(1) 24V not detected on MVL when it should be present. (2) 24V detected on MVH when it should not be present. (3) 24V not detected on MVH when it should be present. (4) 24V not detected on HLO when it should be present. (5) 24V detected on MVL when it should not be. (6) Gas valve relay stuck closed.” What to check	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E11.1	“1st Stage Gas Valve Not Energized When It Should Be Redundant Relay (HLO Output) not Energized when it should be”	Technician	S9VM	FNR-SVX006B-EN p. 106
E11.1	“Gas Valve Relay stuck closed”	Technician	S9VM	FNR-SVX006B-EN p. 106
E11.2	“Communication is lost between the gas valve and the furnace control”	Technician	S9VM	FNR-SVX006B-EN p. 106
E11.3	“The gas valve is responding with incorrect position information.”	Technician	S9VM	FNR-SVX006B-EN p. 106
E11.4	“The gas valve is responding with the incorrect offset information”	Technician	S9VM	FNR-SVX006B-EN p. 106
E12	“Open fuse” What to check	Technician	8 series S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C	FNR-SVN001A-EN p. 46; FNR-SVX002B-EN p. 99; S8XB-SVX001-1D-EN p. 59; FNR-SVX003A-EN p. 59
E12	“Low voltage fuse blown” What to check	Technician	L8V1	FNR-SVX007A-EN p. 43
E12	“Open Low Voltage Fuse” What to check	Technician	S9VM	FNR-SVX006B-EN p. 106
E13	“Blower HP or OEM ID do not match furnace”	Technician	S8V2-C	FNR-SVX003A-EN p. 59
E13	“PM motor information does not match the motor installed”	Technician	L8V1	FNR-SVX007A-EN p. 43
E13	“HP or OEM ID Does Not Match Furnace Model”	Technician	S9VM	FNR-SVX006B-EN p. 106
E13	“HP or OEM ID does not match furnace”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E14	“Configuration file error”	Technician	S8V2-C, S9VM	FNR-SVX003A-EN p. 60; FNR-SVX006B-EN p. 107
E14	“PM is not plugged in”	Technician	L8V1	FNR-SVX007A-EN p. 43
E14	“Configuration File Error No model number has been programmed into the IFC Invalid Model Number”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E15	“Internal PM error”	Technician	L8V1	FNR-SVX007A-EN p. 44
E17	“Blower Communication Error on motor, no communication response”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 46; FNR-SVX006B-EN p. 107
E17	“Blower communication error”	Technician	S8V2-C	FNR-SVX003A-EN p. 60
E17	“IFC Rx not detecting motor feedback”	Technician	L8V1	FNR-SVX007A-EN p. 44
E18	“Blower Communication Error on control, communication lost with blower”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 46; FNR-SVX006B-EN p. 107
E18	“IFC Tx not detecting IFC feedback”	Technician	L8V1	FNR-SVX007A-EN p. 44
E23	“Menu parameters not received by CCM”	Technician	S9V2-VC (Link kit), S8V2-C	FNR-SVN001A-EN p. 46; FNR-SVX003A-EN p. 60
E24	“Internal communication error between the ACM and CCM”	Technician	S8V2-C	FNR-SVX003A-EN p. 60
E24.1	“Communication Lost Between The ACM and CCM, Modbus Communication Error”	Technician	S9VM	FNR-SVX006B-EN p. 107
E24.1	“Communication lost between the ACM and CCM. (Modbus communication)”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E24.2	“CAN Communication Lost”	Technician	S9V2-VC (Link kit), S9VM	FNR-SVN001A-EN p. 46; FNR-SVX006B-EN p. 107
E25	“Orientation sensor out of bounds”	Technician	S8V2-C	FNR-SVX003A-EN p. 60
E25	“Orientation Sensor Out Of Bounds Or Not Responsive”	Technician	S9VM	FNR-SVX006B-EN p. 107
E25	“Accelerometer Out of Bounds or not responsive”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E26	“1) Return static pressure transducer out of bounds 2) Return static pressure transducer configured but not connected”	Technician	S8V2-C	FNR-SVX003A-EN p. 60
E26	“Static Pressure Transducer Out of Bounds or Not Responsive”	Technician	S9VM	FNR-SVX006B-EN p. 107
E26	“Static Pressure transducer out of range”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E27	“1) Return air thermistor out of bounds 2) Return air thermistor configured but not connected”	Technician	S8V2-C	FNR-SVX003A-EN p. 60
E27	“Return Air Thermistor Out Of Range Or Configured ON When Not Installed”	Technician	S9VM	FNR-SVX006B-EN p. 107
E27	“Return thermistor out of range”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
E28	“1) Supply air thermistor out of bounds 2) Supply air thermistor configured but not connected”	Technician	S8V2-C	FNR-SVX003A-EN p. 60
E28	“Supply Air Thermistor Out Of Range Or Configured ON When Not Installed”	Technician	S9VM	FNR-SVX006B-EN p. 107
E28	“Supply thermistor out of range.”	Technician	S9V2-VC (Link kit)	FNR-SVN001A-EN p. 46
Fault LED solid on	“Gas Valve Fault”	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
Fault LED solid on	“Control Failure”	Technician	7 series UHM, DHM, UH3, DH3, (board CNT04829; furnace models not listed), (board CNT05141; furnace models not listed), (board CNT05457; furnace models not listed)	5 documents 18-CD30D1-21-EN p. 55; 18-CD23D1-9 p. 51; 18-CH42D1-2 p. 7; 18-CH46D1-2 p. 7; 18-CH50D1-2 p. 8
Green LED flashing fast	“Normal - Call for Heat”	Owner can check	5 series UH2, DH2, UX2, DX2, *UD2	18-CD26D1-23-EN p. 44; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 29
Green LED flashing slow	“Normal - No call for Heat”	Owner can check	5 series UH2, DH2, UX2, DX2, *UD2	18-CD26D1-23-EN p. 44; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 29
LED continuous off	“Check Power”	Technician	18 series UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1	9 documents 18-CD29D1-18-EN p. 40; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
LED continuous on	“Replace IFC”	Technician	18 series UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1	9 documents 18-CD29D1-18-EN p. 40; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
LED flashing fast	“Normal - Call for Heat”	Owner can check	18 series UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1	9 documents 18-CD29D1-18-EN p. 40; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
LED flashing slow	“Normal - No call for Heat”	Owner can check	18 series UH1, DH1, UH1-H, DH1-H, UC1, DC1, UX1, DX1, UD1, DD1, UD1-H, DD1-H, UE1, DE1, CUX1, CDX1, CUB1, CDB1	9 documents 18-CD29D1-18-EN p. 40; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28
Red LED solid	“Internal GV error or Low TH voltage”	Technician	UX2, DX2, *UD2	18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28

What to check, code by code

Trane and American Standard furnace 2 flashes: system lockout

Checked October 2026

Furnace control LED or display

2 flashes

“System Lockout (Retries or Recycles exceeded)”

Owner checks, then technician

Printed on 21 model series · 12 documents

*UH1, *DH1, *UH1-H, *DH1-H, *UC1, *DC1, *UX1, *DX1, *UD1, *DD1, *UX2, *DX2, *UD2, *UD1-H, *DD1-H, *UE1, *DE1, CUX1, CDX1, CUB1, CDB1 · 18-CD29D1-18-EN p. 40; 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28

Short answer On Trane and American Standard furnaces, 2 flashes mean a lockout after too many ignition retries or flame recycles (communicating models also flash 2 for single retries and recycles). To reset, turn power on-off-on-off twice in 30 seconds; if the code returns, call a servicer. See what to check

What it means

On most Trane boards, two flashes mean a lockout: the control exceeded its number of ignition retries or flame recycles and stopped trying to heat. Most Trane flash lists with a 2-flash row word it as a lockout or as retries or recycles exceeded; on communicating boards the same count also covers single retries and recycles before the lockout:

Table	Series or board	2 flashes, as printed	Source
Single LED and red LED	UC1/DC1, UX1/DX1, UD1/DD1, UH1/DH1, UE1/DE1, the H models of the UD1/DD1 and UH1/DH1, CUX1/CDX1, CUB1/CDB1, UX2/DX2, *UD2	“System Lockout (Retries or Recycles exceeded)”	18-CD19D5-35-EN, p. 40; 18-CD19D6-34, p. 39; 18-CD19D7-29-EN, p. 22; 18-CD29D1-18-EN, p. 40; 18-CD19D4-28-EN, p. 21; 18-CD21D1-15-EN, p. 24; 18-CD33D1-11-EN, p. 39; 41-5016-12, p. 46; 41-5010-25, p. 28; 18-CD19D8-20, p. 37; 18-CD25D1-6, p. 41; 18-CD24D1-6, p. 28
Red LED	UH2/DH2	“RETRIES OR RECYCLES EXCEEDED”	18-CD26D1-23-EN, p. 44
Board guides that list no furnace models	CNT04829, CNT05141, CNT05457	“External lockout (retries or recycles exceeded)”	18-CH42D1-2, p. 6; 18-CH46D1-2, p. 6; 18-CH50D1-2, p. 7
Replacement control kits	the models listed in each kit guide	“SYSTEM LOCKOUT RETRIES OR RECYCLES EXCEEDED”	18-CH76D1-1A-EN, p. 2; 18-CH92D1-1A-EN, p. 2; 18-CH93D1-1A-EN, p. 2; 18-CH111D1-1A-EN, p. 2
Alert tables	UH3/DH3, UHM/DHM and the three boards above	RETRY and RECYCLE, alert code 20, group “Flame lost or Ignition failure”; RETRY LO and RECYCLE LO, alert code 22, group “Soft lockout due to flame lost or ignition retries”	18-CD23D1-9, p. 51; 18-CD30D1-21-EN, p. 55; 18-CH42D1-2, p. 7; 18-CH46D1-2, p. 7; 18-CH50D1-2, p. 8

The alert tables say what the two words mean. A retry is the furnace trying to light without a flame being detected; a recycle is a flame that goes off when it should be detected, after which the furnace tries to relight. On those furnaces 2 flashes also come with single retries and recycles, before any lockout (alert code 20). The lockouts are RETRY LO, after 3 ignition attempts in a row, and RECYCLE LO, after 10 recycles within a single call for heat, each a 1 hour lockout (18-CD30D1-21-EN, p. 55).

Other guides describe the sequence for their own series. On the *UD1/*DD1 and CUB1/CDB1, after a loss of flame the control retries the ignition sequence up to two times after the sensor cools, and locks out the furnace if ignition is not achieved (18-CD19D7-29-EN, p. 22; 41-5010-25, p. 28). The CNT05141 board guide says that in lockout the gas valve is off and the indoor blower and the inducer run at low speed; after one hour in lockout the control resets itself (18-CH46D1-2, p. 3).

Check these first

The owner’s information (32-5083-1C-EN) has no codes, but its troubleshooting table has a row for a lockout. The table goes by symptom; the rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For a lockout: “Turn power on-off-on-off twice in 30 seconds.” (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

The lockout row is the one that relates to a lockout; the other rows are the same on every code page. If the burner does not ignite, the table says to call a servicer, and if the unit still does not operate, to call for a servicer (32-5083-1C-EN, p. 3). Before you call, the start-up section says to turn off the gas to the unit (32-5083-1C-EN, p. 2), with all electric power off before the front panel comes off (32-5083-1C-EN, p. 3): turning off the gas.

Do not try to light the furnace by hand. It has an automatic ignition system, and the manual says not to attempt to light it manually and not to touch the igniter, which is extremely hot (32-5083-1C-EN, p. 2).

When to call a licensed technician

The burner does not ignite (32-5083-1C-EN, p. 3).
The furnace still does not operate after the reset (32-5083-1C-EN, p. 3).
2 flashes come back after the reset. The owner’s information gives no step for codes; these pages send it to the technician.

The flash tables give the meaning only, with no causes or corrective actions (18-CD19D5-35-EN, p. 40; 18-CD26D1-23-EN, p. 44), so there is no technician list to repeat here. The installer’s guides also describe their own resets, worded differently by series; they are listed in the guide as facts about the boards, not as owner steps.

Notes for different models

Series	Code	Wording	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2	E2.1	“Retry Exceeded (Flame never sensed, one hour lockout after 3 times)”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98
the same series	E2.2	“Recycles Exceeded (Flame sensed then lost, one hour lockout after 10 times)”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98
S8V2-C	E2.1	“Retries exceeded (Flame never sensed, one hour lockout after 7 times)”	FNR-SVX003A-EN, p. 59
L8V1	E2.1, E2.2	5 retries, 6 in all, and 9 recycles, 10 in all, each ending in a one hour lockout	FNR-SVX007A-EN, p. 43
S9VM	E2.1, E2.2	“Retries Exceeded - 1 hour lockout”; “Recycles Exceeded - 1 hour lockout”	FNR-SVX006B-EN, p. 104

Trane’s training publication on furnaces built from 1977 to 1991 also lists 2 flashes as a system lockout on the two White-Rodgers boards it describes (34-4054-08, printed pp. 9, 13). The table on this page does not include those boards. The documents do not translate flash counts into display codes.

Trane and American Standard furnace 3 flashes: draft or pressure switch

Checked October 2026

Furnace control LED or display

3 flashes

“Draft Pressure Error - Possible problems: a) Venting problem b) Pressure switch problem c) Inducer problem”

Technician

Printed on 17 model series · 10 documents

*UH1-H, *DH1-H, *UC1, *DC1, *UX1, *DX1, *UX2, *DX2, *UD2, *UD1-H, *DD1-H, *UE1, *DE1, CUX1, CDX1, CUB1, CDB1 · 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD25D1-6 p. 41; 18-CD19D8-20 p. 37; 18-CD24D1-6 p. 28; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28

Short answer On Trane and American Standard furnaces, 3 flashes point to the draft: the tables name venting, pressure switch or inducer problems, depending on the board. Check that the vent terminals are not blocked; the owner's information sends the rest to a qualified service technician. See what to check

What it means

Three flashes point to the furnace’s draft. The single-LED tables and the older red-LED tables print “Draft Pressure Error” with three possible problems: the venting, the pressure switch or the inducer (the induced draft blower). The other tables name the pressure switch, most of them together with the inducer:

Table	Series or board	3 flashes, as printed	Source
Single LED and red LED	UC1/DC1, UX1/DX1, UE1/DE1, the H models of the UD1/DD1 and UH1/DH1, CUX1/CDX1, CUB1/CDB1, UX2/DX2, *UD2	“Draft Pressure Error - Possible problems: a) Venting problem b) Pressure switch problem c) Inducer problem”	18-CD19D5-35-EN, p. 40; 18-CD19D6-34, p. 39; 18-CD19D4-28-EN, p. 21; 18-CD21D1-15-EN, p. 24; 18-CD33D1-11-EN, p. 39; 41-5016-12, p. 46; 41-5010-25, p. 28; 18-CD19D8-20, p. 37; 18-CD25D1-6, p. 41; 18-CD24D1-6, p. 28
Single LED	UH1/DH1, UD1/DD1	the same words without the colon; the UD1/DD1 guide prints “Pressure seitch problem”	18-CD29D1-18-EN, p. 40; 18-CD19D7-29-EN, p. 22
Red LED	UH2/DH2	“INDUCER OR PRESSURE SWITCH ERROR”	18-CD26D1-23-EN, p. 44
Board guides that list no furnace models	CNT04829, CNT05141, CNT05457	“Pressure switch/Inducer error”	18-CH42D1-2, p. 6; 18-CH46D1-2, p. 6; 18-CH50D1-2, p. 7
Replacement control kits	the models listed in each kit guide	“PRESSURE SWITCH FAULT”	18-CH76D1-1A-EN, p. 2; 18-CH92D1-1A-EN, p. 2; 18-CH93D1-1A-EN, p. 2; 18-CH111D1-1A-EN, p. 2
Alert tables	UH3/DH3, UHM/DHM and the three boards above	PS1, PS2 or PS3 OPEN (“Open Pressure Switch”) or CLOSED (“Shorted Pressure Switch”), alert code 1, group “Pressure Switch Failure”	18-CD23D1-9, p. 51; 18-CD30D1-21-EN, p. 55; 18-CH42D1-2, p. 7; 18-CH46D1-2, p. 7; 18-CH50D1-2, p. 8

The CNT05141 and CNT05457 alert tables have no PS3 rows (18-CH46D1-2, p. 7; 18-CH50D1-2, p. 8). On the communicating furnaces, the alert name tells open from shorted and which stage; the count alone does not.

The *UD1/*DD1 and CUB1/CDB1 guides explain what the pressure switch does. If it does not sense pressure, it does not let the gas valve open and the unit does not start; if that happens during a running cycle, it closes the gas valve and shuts the unit down. If pressure against the inducer outlet becomes excessive, as with a flue blockage, the pressure switch shuts off the gas valve until acceptable combustion pressure is available again (18-CD19D7-29-EN, p. 22; 41-5010-25, p. 28). The owner’s information says the same in short: if the furnace cannot exhaust combustion by-products properly, because of a blocked flue hood or other blockage, a pressure switch safety device keeps it from operating (32-5083-1C-EN, p. 2).

Check these first

The owner’s information (32-5083-1C-EN) has no code list and no step for 3 flashes. When a pressure switch keeps the furnace from operating, it says the cause must be investigated by a qualified service technician (32-5083-1C-EN, p. 2).

Its troubleshooting table goes by symptom and does not mention codes. The rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

If the furnace still will not operate, turn off the gas to the unit and call your service technician or gas supplier (32-5083-1C-EN, p. 2). The steps turn off all electric power before the front panel comes off (32-5083-1C-EN, p. 3): turning off the gas.

The list is the same on every code page, and these pages do not present it as a fix for 3 flashes. Venting is one of the three possible problems the flash tables name; the vent terminal check in row 6 is the part of it the owner’s information gives you. Its carbon monoxide warning also asks you to check that the furnace vent and air intake terminals are not obstructed in any way during all seasons (32-5083-1C-EN, p. 3). Apart from the simple maintenance it describes, it says you should not attempt any adjustments or repairs (32-5083-1C-EN, p. 3).

When to call a licensed technician

The pressure switch keeps the furnace from operating: the owner’s information sends the cause to a qualified service technician (32-5083-1C-EN, p. 2).
Checking the venting, the pressure switch and the inducer, the three possible problems in the table (18-CD19D5-35-EN, p. 40).
A restricted or plugged condensate drain (32-5083-1C-EN, p. 3).
3 flashes keep coming back. The owner’s information gives no step for codes; these pages send it to the technician.

The flash tables have no column of corrective actions (18-CD19D5-35-EN, p. 40; 18-CD26D1-23-EN, p. 44), so there is no technician list to repeat here.

Notes for different models

Series	Code	Wording	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2, S8V2-C, S9V2-VC (Link kit), S9VM	E3.1	“Shorted Pressure Switch, 1st Stage”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98; FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105
the same series	E3.2	“Open Pressure Switch, 1st Stage”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98; FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105
S9X2 (not S9X1, S9B1)	E3.3, E3.4	second stage pressure switch shorted or open	FNR-SVX002B-EN, p. 98
S9VM	E3.0, E3.5 to E3.8	combustion pressure alerts; combustion transducer out of bounds	FNR-SVX006B-EN, p. 105
L8V1	E3.1 to E3.3	listed under “Pressure Transducer Error”	FNR-SVX007A-EN, p. 43
S9X1, S9X2, S9B1	E09	“Open Inducer Limit Switch or Condensate Pressure Switch”	FNR-SVX002B-EN, p. 98

On boards where 9 flashes is an open inducer limit, that is a different switch from the pressure switch in this code (18-CD19D8-20, p. 37); see 9 flashes. The documents do not translate flash counts into display codes.

Trane and American Standard furnace 4 flashes: limit or rollout open

Checked October 2026

Furnace control LED or display

4 flashes

“Open Temperature Limit Circuit”

Technician

Printed on 16 model series · 8 documents

*UH1-H, *DH1-H, *UC1, *DC1, *UX1, *DX1, *UD1, *DD1, *UD1-H, *DD1-H, *UE1, *DE1, CUX1, CDX1, CUB1, CDB1 · 18-CD33D1-11-EN p. 39; 18-CD19D5-35-EN p. 40; 18-CD19D6-34 p. 39; 18-CD19D7-29-EN p. 22; 18-CD21D1-15-EN p. 24; 18-CD19D4-28-EN p. 21; 41-5016-12 p. 46; 41-5010-25 p. 28

Short answer On Trane and American Standard furnaces, 4 flashes mean an open limit; the *UH2/*DH2 and boards CNT04829, CNT05141 and CNT05457 also name the rollout switch (see the table below). The owner's information sends both switches to a qualified service technician. See what to check

What it means

Four flashes report a limit or rollout fault, and some rows add the flame rollout switch. The words depend on the series and the board:

Table	Series or board	4 flashes, as printed	Source
Single LED	UC1/DC1, UX1/DX1, UD1/DD1, UE1/DE1, the H models of the UD1/DD1 and UH1/DH1, CUX1/CDX1, CUB1/CDB1	“Open Temperature Limit Circuit”	18-CD19D5-35-EN, p. 40; 18-CD19D6-34, p. 39; 18-CD19D7-29-EN, p. 22; 18-CD19D4-28-EN, p. 21; 18-CD21D1-15-EN, p. 24; 18-CD33D1-11-EN, p. 39; 41-5016-12, p. 46; 41-5010-25, p. 28
Single LED	UH1/DH1	“Open High Limit Device”	18-CD29D1-18-EN, p. 40
Red LED	UX2/DX2, *UD2	“Open Temperature Limit Switch”	18-CD19D8-20, p. 37; 18-CD25D1-6, p. 41; 18-CD24D1-6, p. 28
Red LED	UH2/DH2	“OPEN LIMIT OR ROLLOUT SWITCH”	18-CD26D1-23-EN, p. 44
Board guides that list no furnace models	CNT04829, CNT05141, CNT05457	“Open limit switch & Aux & Rollout”	18-CH42D1-2, p. 6; 18-CH46D1-2, p. 6; 18-CH50D1-2, p. 7
Replacement control kits	the models listed in each kit guide	“OPEN LIMIT SWITCH”	18-CH76D1-1A-EN, p. 2; 18-CH92D1-1A-EN, p. 2; 18-CH93D1-1A-EN, p. 2; 18-CH111D1-1A-EN, p. 2
Alert tables	UH3/DH3, UHM/DHM and the three boards above	HIGH LIMIT and AUX LIMIT, alert code 26, group “High Temp Limit Fault”; ROLLOUT OPEN, alert code 87, group “Roll Out Fault”	18-CD23D1-9, p. 51; 18-CD30D1-21-EN, p. 55; 18-CH42D1-2, p. 7; 18-CH46D1-2, p. 7; 18-CH50D1-2, p. 8

The flash tables give only the meaning, with no causes. The alert tables add a description: HIGH LIMIT is the high limit and AUX LIMIT the reverse flow limit, both with the heat exchanger temperature too high, which the table says “Could be caused by low airflow or fan failure.”; ROLLOUT OPEN is “Open flame rollout” (18-CD30D1-21-EN, p. 55).

The owner’s information describes both kinds of switch, without codes. The limit is an automatic reset safety control that prevents overheating: when it opens, it shuts down the heating circuit until the unit cools down, and inadequate airflow may make the unit cycle on and off as the limit trips and resets (32-5083-1C-EN, p. 2). If flames from the burner are not properly drawn into the heat exchanger, a flame rollout protection control opens and shuts the furnace off (32-5083-1C-EN, p. 2).

Check these first

The owner’s information (32-5083-1C-EN) has no code list and no step for 4 flashes. For the two switches above it gives one instruction each: if you suspect the unit is cycling on its limit control, contact a qualified service technician immediately for instructions, and when the rollout control opens, the cause must be investigated by a qualified service technician (32-5083-1C-EN, p. 2).

Its troubleshooting table goes by symptom and does not mention codes. The rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

The list is the same on every code page, and these pages do not present it as a fix for 4 flashes. The owner’s information says that apart from the simple maintenance it describes, such as the filters, you should not attempt any adjustments or repairs, and never to remove a panel while the unit is operating (32-5083-1C-EN, p. 3).

When to call a licensed technician

The furnace cycles on its limit control, or the rollout control has opened (32-5083-1C-EN, p. 2).
Finding why the switch opened. The flash tables give no causes; the alert tables point to low airflow or fan failure for the limit alerts (18-CD30D1-21-EN, p. 55).
A burner box limit. The *UX2/*DX2, *UH3/*DH3 and *UHM/*DHM guides describe a manual reset temperature limit on the bottom of the burner box. Its reset button is pressed only after the vent and combustion air inlet terminations have been checked and a blockage cleared; with no blockage, the *UX2/*DX2 guide says the limit must be reset by a qualified servicer, and the *UH3/*DH3 and *UHM/*DHM guides say not to reset it and to call a qualified service professional (18-CD19D8-20, p. 36; 18-CD23D1-9, p. 49; 18-CD30D1-21-EN, p. 53). The guides do not say which flash code this limit causes. The switch is inside the cabinet and the owner’s information does not mention it, so these pages leave it to a technician.
4 flashes keep coming back. The owner’s information gives no step for codes; these pages send it to the technician.

Notes for different models

Series or board	Code	Wording	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2	E04	“Open Limit (Main Thermal, Rollout Switch, or Reverse Airflow Switch)”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98
L8V1	E04	“A thermal limit has opened in the safety circuit”	FNR-SVX007A-EN, p. 43
S8V2-C	E4.0, E4.1, E4.2	“Open high limit switch”; “Open reverse air-flow limit switch”; “Open roll-out limit switch”	FNR-SVX003A-EN, p. 59
S9V2-VC (Link kit), S9VM	E4.0, E4.1, E4.2	“Open High Limit”; “Open Reverse Airflow Limit”; “Open Rollout Limit”	FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105
UH3/DH3, UHM/DHM, board CNT04829	9 flashes, IND LIMIT	alert code 26, “High Temp Limit Fault”: “Flue gas temperature too high. Could be caused by low airflow or fan failure.”	18-CD30D1-21-EN, p. 55; 18-CD23D1-9, p. 51; 18-CH42D1-2, p. 7

On the communicating furnaces, alert code 26 can come with 4 flashes (HIGH LIMIT, AUX LIMIT) or with 9 flashes (IND LIMIT) (18-CD30D1-21-EN, p. 55). On a furnace whose control was replaced with one of Trane’s igniter conversion kits, the kit’s table applies (18-CH111D1-1A-EN, p. 2); more on the kits in the guide. The documents do not translate flash counts into display codes.

Trane and American Standard furnace 9 flashes: igniter relay or inducer limit

Checked October 2026

Furnace control LED or display

9 flashes

“Ignitor Relay Fault”

Technician

Printed on 6 model series · 3 documents

*UH1, *DH1, *UC1, *DC1, *UD1, *DD1 · 18-CD29D1-18-EN p. 40; 18-CD19D5-35-EN p. 40; 18-CD19D7-29-EN p. 22

Short answer On Trane and American Standard furnaces, 9 flashes mean different things by board: an igniter relay fault, an igniter circuit check with a possible grounding problem, or an open inducer limit; find your series in the table below. All of these are technician work. See what to check

What it means

Nine flashes do not have one meaning. Depending on the board, Trane’s tables give an igniter relay fault, a check of the igniter circuit with a possible grounding problem, or an open inducer limit switch, and some tables have no 9-flash row at all. The box above shows the first row of the table on this site, Ignitor Relay Fault on the *UC1/*DC1, *UD1/*DD1 and *UH1/*DH1. Find your series or board:

Table	Series or board	9 flashes, as printed	Source
Single LED	UC1/DC1, UD1/DD1, UH1/DH1	“Ignitor Relay Fault” (the UD1/DD1 and UH1/DH1 guides print “Ignitor relay fault”)	18-CD19D5-35-EN, p. 40; 18-CD19D7-29-EN, p. 22; 18-CD29D1-18-EN, p. 40
Single LED	UX1/DX1, the H models of the UD1/DD1	“Check Ignitor Circuit and Line “N” to 24VAC “Common” voltage (≤ 2 volts) [possible grounding problem]”	18-CD19D6-34, p. 39; 18-CD21D1-15-EN, p. 24
Single LED	the H models of the UH1/DH1	the same words with “(< 2 volts)”	18-CD33D1-11-EN, p. 39
Single LED	UE1/DE1, CUX1/CDX1, CUB1/CDB1	no 9-flash row; the lists end at 8 flashes	18-CD19D4-28-EN, p. 21; 41-5016-12, p. 46; 41-5010-25, p. 28
Red LED	UX2/DX2, *UD2	“Open Inducer Limit switch”	18-CD19D8-20, p. 37; 18-CD25D1-6, p. 41; 18-CD24D1-6, p. 28
Red LED	UH2/DH2	“OPEN INDUCER LIMIT ERROR”	18-CD26D1-23-EN, p. 44
Board guides that list no furnace models	CNT04829, CNT05457	“Open Inducer Limit Switch”	18-CH42D1-2, p. 6; 18-CH50D1-2, p. 7
Board guide that lists no furnace models	CNT05141	no 9-flash row	18-CH46D1-2, p. 6
Replacement control kits 18109, 18110, 20350	the models listed in each kit guide	“IGNITER RELAY FAULT”	18-CH92D1-1A-EN, p. 2; 18-CH93D1-1A-EN, p. 2; 18-CH111D1-1A-EN, p. 2
Replacement control kit 17399	UD2/DD2 models in the kit guide	“OPEN INDUCER LIMIT”	18-CH76D1-1A-EN, p. 2
Alert tables	UH3/DH3, UHM/DHM, board CNT04829	IND LIMIT, alert code 26, group “High Temp Limit Fault”: “Flue gas temperature too high. Could be caused by low airflow or fan failure.”	18-CD23D1-9, p. 51; 18-CD30D1-21-EN, p. 55; 18-CH42D1-2, p. 7

The “Check Ignitor Circuit” rows are an instruction to measure a voltage. They are a technician’s check, not an owner step.

The same furnace can have two answers. The *UX2/*DX2 guide gives 9 flashes as “Open Inducer Limit switch” (18-CD19D8-20, p. 37). Kit 20350 replaces the control on *UX2/*DX2 models, and its table gives “IGNITER RELAY FAULT” (18-CH111D1-1A-EN, pp. 1–2). On the *UH1/*DH1 and *UD1/*DD1, kit 18110’s table and the furnaces’ own guides both give an igniter relay fault (18-CH93D1-1A-EN, p. 2; 18-CD29D1-18-EN, p. 40; 18-CD19D7-29-EN, p. 22). The kit guides ask the installer to sign a label and attach it to the front of the blower door (18-CH111D1-1A-EN, p. 2); they do not show what the label says.

One board disagrees with its own alert table. CNT05457’s flash list has 9 flashes for an open inducer limit (18-CH50D1-2, p. 7), but its alert table, like that of the CNT05141, has no IND LIMIT row (18-CH50D1-2, p. 8; 18-CH46D1-2, p. 7).

Check these first

The owner’s information (32-5083-1C-EN) has no code list and no step for 9 flashes. Do not touch the igniter: the manual says it is extremely hot, and that the furnace has automatic ignition and must not be lit by hand (32-5083-1C-EN, p. 2).

Its troubleshooting table goes by symptom and does not mention codes. The rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

The list is the same on every code page, and these pages do not present it as a fix for 9 flashes.

When to call a licensed technician

Any of the 9-flash meanings. The flash tables give no corrective actions, and the igniter circuit check is a voltage measurement.
On the communicating furnaces, finding why the inducer limit opened; the alert table names flue gas temperature too high, possibly from low airflow or fan failure (18-CD30D1-21-EN, p. 55).
9 flashes keep coming back. The owner’s information gives no step for codes; these pages send it to the technician.

Notes for different models

Series	Code	Wording	Source
S9X1, S9X2, S9B1	E09	“Open Inducer Limit Switch or Condensate Pressure Switch”	FNR-SVX002B-EN, p. 98
S9V2-VC (Link kit), S9VM	E9.1	“Open Inducer Limit Switch”	FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 106
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2	E6.3	“(1) Igniter relay fails (2) Igniter open”	S8XB-SVX001-1D-EN, p. 59; FNR-SVX002B-EN, p. 98

For the display codes, the S9X troubleshooting charts say an inducer limit error is normally caused by improper installation or application of the furnace venting system (FNR-SVX002B-EN, p. 111), and define an igniter relay fault as the control sensing that the igniter relay has stuck closed (FNR-SVX002B-EN, p. 109). Those definitions are for the S9X series. The documents do not translate flash counts into display codes.

Trane and American Standard furnace E2.1: retries exceeded, lockout

Checked October 2026

Furnace control LED or display

E2.1

“Retry Exceeded (Flame never sensed, one hour lockout after 3 times)”

Owner checks, then technician

Printed on 6 model series · 2 documents

S9X1, S9X2, S9B1, S8B1, S8X1, S8X2 · FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58

Short answer On Trane and American Standard S-Series and L8V1 furnaces, E2.1 means no flame was sensed in the allowed tries, which differ by series, and a one-hour lockout followed. Reset by turning power on-off-on-off twice in 30 seconds; if it returns, call a servicer. See what to check

What it means

E2.1 means the furnace tried to light and the control never sensed a flame, so after the allowed number of tries it locked out for one hour. The number of tries depends on the series:

Series	E2.1, as printed	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2	“Retry Exceeded (Flame never sensed, one hour lockout after 3 times)”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98
S8V2-C	“Retries exceeded (Flame never sensed, one hour lockout after 7 times)”	FNR-SVX003A-EN, p. 59
L8V1	“Flame never sensed (5 retries, 6 total results in one hour lockout)”	FNR-SVX007A-EN, p. 43
S9VM	“Retries Exceeded - 1 hour lockout”	FNR-SVX006B-EN, p. 104
S9V2-VC (Link kit)	“Retry exceeded”	FNR-SVN001A-EN, p. 45

The troubleshooting charts count the tries within a single call for heat. The S9X chart: 3 unsuccessful tries for ignition within a single call for heat, a lockout period of one hour, and the flame has never been sensed (FNR-SVX002B-EN, p. 102). The S8V2-C chart says 6 tries, while its own table says 7 (FNR-SVX003A-EN, pp. 59, 64). For the S9V2 the Link kit chart says 6 (FNR-SVN001A-EN, p. 48), and the chart in the S9V2’s own IOM says 3 (FNR-SVX001C-EN, p. 84).

E2.2 is the other flame lockout: there the flame was sensed and then lost, and the lockout comes after 10 recycles (S8XB-SVX001-1D-EN, p. 58).

Trane’s tables draw the code in seven-segment characters as E2_1, with a low bar where the text has a point (18-CE04D1-1D-EN, p. 58). The S9VM pairs it with communication code ERR.022.01 (FNR-SVX006B-EN, p. 104).

Check these first

The owner’s information (32-5083-1C-EN) has no codes, but its troubleshooting table has a row for a lockout. The table goes by symptom; the rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For a lockout: “Turn power on-off-on-off twice in 30 seconds.” (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

The lockout row is the one that matches this code; the other rows are the same on every code page. If the burner does not ignite, the table says to call a servicer, and if the unit still does not operate, to call for a servicer (32-5083-1C-EN, p. 3). Before you call, the start-up section says to turn off the gas to the unit (32-5083-1C-EN, p. 2), with all electric power off before the front panel comes off (32-5083-1C-EN, p. 3): turning off the gas.

When to call a licensed technician

The burner does not ignite, or the furnace still does not operate after the reset (32-5083-1C-EN, p. 3).
E2.1 comes back. The owner’s information gives no step for codes; these pages send it to the technician.

Two tables list causes for their own series, all of them technician work. The L8V1 table: the gas valve not energized, a faulty flame sensor, low manifold pressure (FNR-SVX007A-EN, p. 43). The S9VM table: the flame sensor not sensing flame or not positioned properly in the flame, inlet or outlet gas pressure too low, and burner crossovers not aligned properly or restricted (FNR-SVX006B-EN, p. 104). Gas pressure checks belong to the technician; the owner’s information says that apart from the simple maintenance it describes, you should not attempt any adjustments or repairs (32-5083-1C-EN, p. 3).

Notes for different models

Series	Code	Wording	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2	E2.2	“Recycles Exceeded (Flame sensed then lost, one hour lockout after 10 times)”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98
the same series	E2.3	“1st Stage Gas Valve Not Energized When It Should Be exceeded after 10 times”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98
L8V1	E2.4	“HLO relay not energized when it should be”	FNR-SVX007A-EN, p. 43
S9VM	E2.4	“General Gas Valve Lockout”	FNR-SVX006B-EN, p. 104
LED boards	2 flashes	a lockout after retries or recycles exceeded	18-CD19D5-35-EN, p. 40; 18-CD26D1-23-EN, p. 44
UH3/DH3, UHM/DHM	2 flashes, RETRY LO	“3 ignition attempts in a row within a single call for heat results in 1 hr lockout.”	18-CD30D1-21-EN, p. 55

The lockout reset above is from the owner’s information, the one owner’s document Trane and American Standard link for all their gas heating systems (32-5083-1C-EN, p. 3). The documents do not translate flash counts into display codes.

Related codes: E2.2, E2.3, E08. All Trane and American Standard codes

Trane and American Standard furnace E3.1: shorted pressure switch

Checked October 2026

Furnace control LED or display

E3.1

“Shorted Pressure Switch, 1st Stage”

Technician

Printed on 9 model series · 5 documents

S9V2-VC (Link kit), S9X1, S9X2, S9B1, S8B1, S8X1, S8X2, S8V2-C, S9VM · FNR-SVN001A-EN p. 45; FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58; FNR-SVX003A-EN p. 59; FNR-SVX006B-EN p. 105

Short answer On Trane and American Standard S-Series furnaces, E3.1 means the first stage pressure switch is closed when it should be open; on the L8V1 it is a pressure transducer signal that is not present. Checking the switch wiring and tubing is technician work. See what to check

What it means

E3.1 means the control found the first stage pressure switch closed at a time when it should be open. Trane’s S-Series tables call it “Shorted Pressure Switch, 1st Stage” (S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98; FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105). The troubleshooting charts define it the same way, say that in most cases the pressure switch is not the problem, and add a note to verify that the pressure switch wiring and tube routing are correct (FNR-SVX002B-EN, p. 103; S8XB-SVX001-1D-EN, p. 65; FNR-SVX003A-EN, p. 66).

The opposite case is E3.2, “Open Pressure Switch, 1st Stage”: the switch is open when it should be closed (FNR-SVX002B-EN, pp. 98, 104). E3.3 and E3.4 are the same two faults for the second stage switch; the S9X table marks them “Not applicable for S9X1/S9B1” (FNR-SVX002B-EN, p. 98).

On the L8V1, E3.1 means something else. Its table lists E3.1 to E3.3 under “Pressure Transducer Error”, and E3.1 there is a transducer signal that is not present (FNR-SVX007A-EN, p. 43).

Trane’s tables draw the code in seven-segment characters as E3_1, with a low bar where the text has a point (18-CE04D1-1D-EN, p. 58). The S9VM pairs it with communication code ERR.001.05 (FNR-SVX006B-EN, p. 105).

Check these first

The owner’s information (32-5083-1C-EN) has no code list and no step for E3.1. It mentions the pressure switch only as a safety device that keeps the furnace from operating when combustion by-products cannot be exhausted properly, and says the cause must be investigated by a qualified service technician (32-5083-1C-EN, p. 2).

Its troubleshooting table goes by symptom and does not mention codes. The rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

The list is the same on every code page, and these pages do not present it as a fix for E3.1. The checks the charts name for this code are on the pressure switch, its wiring and its tubing (FNR-SVX002B-EN, p. 103).

When to call a licensed technician

Checking the pressure switch wiring and tube routing, as the charts ask (FNR-SVX002B-EN, p. 103).
The causes the S9VM table lists for its own E3.1: pressure switch contacts stuck closed, the draft inducer motor running with no call for heat, and improper wiring to the pressure switch (FNR-SVX006B-EN, p. 105). That list is for the S9VM only.
On the L8V1, the transducer checks in its table, which include voltage measurements (FNR-SVX007A-EN, p. 43).
E3.1 keeps coming back. The owner’s information gives no step for codes; these pages send it to the technician.

The owner’s information says that apart from the simple maintenance it describes, you should not attempt any adjustments or repairs (32-5083-1C-EN, p. 3).

Notes for different models

Series or board	Code	Wording	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2, S8V2-C, S9V2-VC (Link kit), S9VM	E3.1	“Shorted Pressure Switch, 1st Stage” (S8V2-C: “Shorted pressure switch, 1st stage”)	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98; FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105
S8B1, 2020 guide	E3.1	“Shorted Pressure Switch”	18-CE09D1-1E-EN, p. 54
L8V1	E3.1	a pressure transducer signal not present	FNR-SVX007A-EN, p. 43
S9VM	E3.0, E3.5 to E3.8	combustion pressure alerts; combustion transducer out of bounds	FNR-SVX006B-EN, p. 105
UH3/DH3, UHM/DHM and boards CNT04829, CNT05141, CNT05457	3 flashes, PS1 CLOSED	alert code 1, “Shorted Pressure Switch, first stage”	18-CD30D1-21-EN, p. 55; 18-CD23D1-9, p. 51; 18-CH46D1-2, p. 7
other LED boards	3 flashes	draft pressure, pressure switch or inducer error	18-CD19D5-35-EN, p. 40; 18-CD26D1-23-EN, p. 44

On the S8 series, the newer tables mark E3.3 and E3.4 “Not Applicable for S8B1, S8X1” and the 2020 tables “S8X2 only” (S8XB-SVX001-1D-EN, p. 58; 18-CE04D1-1D-EN, p. 58). The documents do not translate flash counts into display codes.

Trane and American Standard furnace error code E04: open limit

Checked October 2026

Furnace control LED or display

E04

“Open Limit (Main Thermal, Rollout Switch, or Reverse Airflow Switch)”

Technician

Printed on 6 model series · 2 documents

S9X1, S9X2, S9B1, S8B1, S8X1, S8X2 · FNR-SVX002B-EN p. 98; S8XB-SVX001-1D-EN p. 58

Short answer On Trane and American Standard S8 and S9X furnaces, E04 means an open limit: the main thermal, rollout or reverse airflow switch; the L8V1 words it as a thermal limit open in the safety circuit. Finding which one opened is technician work. See what to check

What it means

E04 on the furnace’s seven-segment display means a limit in the safety circuit has opened. The S8 and S9X tables name the three switches it can be: the main thermal limit, the rollout switch or the reverse airflow switch (S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98). The L8V1 table words it as a thermal limit that has opened in the safety circuit (FNR-SVX007A-EN, p. 43). The S9X troubleshooting chart describes limit switches as safety devices that open when an abnormal high temperature has been sensed (FNR-SVX002B-EN, p. 106).

Three other series split the code by switch, with a digit after the point: E4.0 is the high limit, E4.1 the reverse airflow limit and E4.2 the rollout limit on the S8V2-C, on the S9V2 with the Link kit and on the S9VM (FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105). Searches for “E4” (Google autocomplete, checked October 21, 2026) most likely mean E04 or one of these three.

The owner’s information describes the two kinds of switch without codes. The limit is an automatic reset safety control that prevents overheating: when it opens, it shuts down the heating circuit until the unit cools down, and inadequate airflow may make the unit cycle on and off as the limit trips and resets. If flames from the burner are not properly drawn into the heat exchanger, a flame rollout protection control opens and shuts the furnace off (32-5083-1C-EN, p. 2).

Check these first

The owner’s information (32-5083-1C-EN) has no code list and no step for E04. For the two switches above it gives one instruction each: if you suspect the unit is cycling on its limit control, contact a qualified service technician immediately for instructions, and when the rollout control opens, the cause must be investigated by a qualified service technician (32-5083-1C-EN, p. 2).

Its troubleshooting table goes by symptom and does not mention codes. The rows an owner can act on, in the table’s order:

Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3).
If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
Make sure the blower door is closed securely; the table says this restores power to the blower and gas valve (32-5083-1C-EN, p. 3).
For heat that is not enough while the blower runs all the time: clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
For no heat while the vent motor runs: make sure the vent terminals are not blocked; a restricted or plugged condensate drain is for a servicer (32-5083-1C-EN, p. 3).

The list is the same on every code page, and these pages do not present it as a fix for E04. The technician tables for two series do name the filter among the causes (see below), and filter care is part of the maintenance the owner’s information leaves to you: replace disposable filters every month, twice a month in seasons when the unit runs more often, and never run the furnace without them (32-5083-1C-EN, p. 3).

When to call a licensed technician

The furnace cycles on its limit control, or the rollout control has opened (32-5083-1C-EN, p. 2).
Finding which limit opened and why. On the L8V1 the table’s cause column says a primary, burner box or reverse airflow limit tripped, and lists a dirty filter or restricted airflow for the primary limit, and high manifold pressure, a clogged burner inlet or a dirty burner system for the burner box limit (FNR-SVX007A-EN, p. 43).
On the S9X series, the chart for 04 includes verifying that the filters and blower wheels are clean (FNR-SVX002B-EN, p. 106).
E04 keeps coming back. The owner’s information gives no step for codes; these pages send it to the technician.

The causes in these tables, such as gas pressure, burners and the limit switches, are technician work. The owner’s information says that apart from the simple maintenance it describes, you should not attempt any adjustments or repairs (32-5083-1C-EN, p. 3).

Notes for different models

Series	Code	Wording	Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2	E04	“Open Limit (Main Thermal, Rollout Switch, or Reverse Airflow Switch)”	S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98; 18-CE09D1-1E-EN, p. 54
L8V1	E04	“A thermal limit has opened in the safety circuit”	FNR-SVX007A-EN, p. 43
S8V2-C	E4.0, E4.1, E4.2	“Open high limit switch”; “Open reverse air-flow limit switch”; “Open roll-out limit switch”	FNR-SVX003A-EN, p. 59
S9V2-VC (Link kit), S9VM	E4.0, E4.1, E4.2	“Open High Limit”; “Open Reverse Airflow Limit”; “Open Rollout Limit”	FNR-SVN001A-EN, p. 45; FNR-SVX006B-EN, p. 105
LED boards	4 flashes	an open limit, on some boards limit or rollout	18-CD19D5-35-EN, p. 40; 18-CD26D1-23-EN, p. 44

On the S9VM the table gives its own causes. For E4.0: low airflow across the heat exchanger, a dirty evaporator coil, a dirty return air filter, a dirty blower wheel, outlet gas pressure set too high, or return air above 80 °F (about 27 °C). For E4.1: the blower not operating correctly, an airflow setting too low, or a blower off delay that is not long enough. For E4.2: a missing cold header plug or inducer cap, burner flame impingement, a draft inducer not operating properly, a restricted heat exchanger, low outlet gas pressure, or a gas valve that does not fully close (FNR-SVX006B-EN, p. 105). That list is for the S9VM only.

The S8 table calls the code E04, while the S8 troubleshooting charts are headed “4.0 Fault Code” (S8XB-SVX001-1D-EN, pp. 58, 69–70). The S9V2’s own IOM has no code table, only flow charts (FNR-SVX001C-EN, pp. 83–94); the S9V2 row above comes from the Link kit guide.

Related codes: E4.0, E4.2, E09. All Trane and American Standard codes

How to read a Trane or American Standard furnace code

These pages cover Trane and American Standard gas furnaces. Trane publishes one set of documents for both brands: the last page of its current manuals is headed “About Trane and American Standard Heating and Air Conditioning” (FNR-SVX002B-EN, p. 120; 32-5083-1C-EN, p. 4), and for all gas heating systems trane.com and americanstandardair.com link the same owner’s information, 32-5083-1C-EN (both owner’s manual pages checked October 21, 2026). That owner’s information has no codes (32-5083-1C-EN, pp. 1–4). The code tables are in the installer’s guides and the installation, operation and maintenance (IOM) manuals, and the way a code is shown depends on the furnace’s control board.

One LED that counts flashes

Older installer’s guides print “Integrated Furnace Control Error Flash Codes” for one diagnostic LED and do not name its color. Slow flashing is normal with no call for heat, fast flashing is normal with a call for heat, a light that stays on reads “Replace IFC” (IFC is the integrated furnace control), a light that stays off reads “Check Power”, and 2 to 8 or 2 to 9 flashes are faults (18-CD19D5-35-EN, p. 40; 41-5010-25, p. 28). The table on this page has this kind of list for the *UC1/*DC1, *UX1/*DX1, *UD1/*DD1, *UH1/*DH1 and *UE1/*DE1, the H models of the *UD1/*DD1 and *UH1/*DH1, and the CUX1/CDX1 and CUB1/CDB1.

Red and green LEDs

The guides for the *UX2/*DX2, *UD2 and *UH2/*DH2 list two LEDs: a red “ERROR” LED that flashes the count, and a green “STATUS” LED that flashes slowly when there is no call for heat and fast when there is one (18-CD19D8-20, p. 37; 18-CD24D1-6, pp. 28–29; 18-CD26D1-23-EN, p. 44). One red flash every 20 seconds is normal. The guides call it LitePort data (18-CD19D8-20, p. 37), and Trane’s replacement control kits list 1 flash as “NORMAL OPERATION - Flash every 20 seconds” (18-CH93D1-1A-EN, p. 2).

At power-up these controls replay the last four faults on the red LED, newest first, with a 2 second pause between codes, while the green LED stays on (18-CD19D8-20, p. 37). A count seen right after the power comes back can be a stored fault, not the current one. Codes shown as a steady red light are not replayed (18-CD19D8-20, p. 37).

Both LEDs lit together is listed as “FUSE OPEN OR INTERNAL CONTROL FAILURE” on the *UH2/*DH2 (18-CD26D1-23-EN, p. 44) and as “Continuous Reset caused by a blown fuse or internal error.” on the *UX2/*DX2 (18-CD19D8-20, p. 37).

Communicating furnaces: flash counts and alert codes

The communicating *UH3/*DH3 and *UHM/*DHM furnaces and the replacement boards CNT04829, CNT05141 and CNT05457 have four LEDs: a red alert LED that flashes the count, a green STATUS LED (fast flash for a call for heat, slow flash for none), a green BM LED that is on whenever the unit has power, and an amber COM LED that flashes the device count (18-CD23D1-9, p. 50; 18-CH46D1-2, p. 6). On the CNT05141 board a code flash is about 1/4 second on and 1/4 second off, with about 2 seconds between groups (18-CH46D1-2, p. 6). These controls also replay their last four alerts at power-up (18-CD23D1-9, p. 50).

On these furnaces a flash count stands for a group of alerts. The alert tables give each alert a name shown on the furnace’s User Interface, an alert code number and a group. 4 flashes, for example, covers HIGH LIMIT and AUX LIMIT (alert code 26) and ROLLOUT OPEN (alert code 87) (18-CD30D1-21-EN, p. 55). The guides say alert codes appear as a text message on the User Interface menu and as an alert code number on the comfort control display (18-CD30D1-21-EN, p. 54). Some alerts have no flash count: “24V Fuse Open”, alert code 92, has “None” in the Fault LED column (18-CD30D1-21-EN, p. 55).

S-Series and L8V1: the seven-segment display

The S8B1, S8X1, S8X2, S9B1, S9X1, S9X2, S9V2, S8V2-C and L8V1 show codes on a seven-segment display on the control (18-CE04D1-1D-EN, p. 59; FNR-SVX002B-EN, p. 98; FNR-SVX003A-EN, p. 59; FNR-SVX007A-EN, p. 41; FNR-SVN001A-EN, p. 46). It shows status symbols, and when an error occurs, an E-code alternates with the system mode and the airflow (FNR-SVX001C-EN, p. 81). The S9VM table uses the same kind of E-codes (FNR-SVX006B-EN, pp. 104–107). Trane’s tables draw the codes in seven-segment characters, where the point between the digits is a low bar: E2_1 in the table is E2.1 in the text of other Trane documents (18-CE04D1-1D-EN, p. 58; FNR-SVX006B-EN, p. 104). These pages write E2.1. The S9V2 Link kit guide adds that in downflow orientation the decimal points are at the top of the display (FNR-SVN001A-EN, p. 46).

Letters on their own are status symbols, not faults. In the S8 table, IdL is idle, Ht1 and Ht2 are first and second stage heating, CL1 and CL2 cooling, HP1 and HP2 heat pump, Err is the active alarm menu and L6F the last 6 faults (S8XB-SVX001-1D-EN, p. 58). On the L8V1, ARF is the calculated airflow, followed by the airflow times 10, and C0F is continuous fan (FNR-SVX007A-EN, p. 41). Searches for “1dl”, “arf” or “cof” (Google autocomplete, checked October 21, 2026) most likely mean these symbols. Viewing and clearing the stored faults is done with the Menu and Option buttons on the control, in steps written for the installer (18-CE04D1-1D-EN, p. 59); these pages do not repeat them.

An S9V2 converted with Trane’s Link kit (S9V2-VC) shows only two digits: codes 10.1 to 10.4 appear as E10, and 24.1 and 24.2 as E24. The full code is read over Bluetooth with the Technician app or on the SC360 thermostat (FNR-SVN001A-EN, p. 46). The S9VM table pairs each display code with a communication code, such as ERR.022.01 for E2.1 (FNR-SVX006B-EN, p. 104).

What the table leaves out

Several IOM manuals also have troubleshooting flow charts for the codes, written for technicians (FNR-SVX002B-EN, pp. 102–112). The table on this page quotes the code tables, not the charts. The S9V2’s own documents have no code table: its 2022 installer’s guide lists the display symbols only (18-CE19D1-1B-EN, pp. 97–101), and its 2026 IOM gives the codes as flow charts (FNR-SVX001C-EN, pp. 83–94). The S9V2-VC (Link kit) rows in the table come from the guide for the Link kit (FNR-SVN001A-EN, pp. 45–46).

Trane’s training publication on furnaces built from 1977 to 1991 describes older White-Rodgers boards with their own LED codes (34-4054-08, printed pp. 9, 13). It says it is not to be used for specific service procedures (34-4054-08, printed p. 1), and the table leaves it out.

Why a flash count needs the series

The same count means different things on different boards. Four of Trane’s tables, quoted as printed (*UC1/*DC1: 18-CD19D5-35-EN, p. 40; *UX2/*DX2: 18-CD19D8-20, p. 37; *UH2/*DH2: 18-CD26D1-23-EN, p. 44; board CNT05141: 18-CH46D1-2, p. 6):

Flashes	Single LED, UC1/DC1	Red LED, UX2/DX2	Red LED, UH2/DH2	Board CNT05141
3	“Draft Pressure Error - Possible problems: a) Venting problem b) Pressure switch problem c) Inducer problem”	same as UC1/DC1	“INDUCER OR PRESSURE SWITCH ERROR”	“Pressure switch/Inducer error”
4	“Open Temperature Limit Circuit”	“Open Temperature Limit Switch”	“OPEN LIMIT OR ROLLOUT SWITCH”	“Open limit switch & Aux & Rollout”
6	“115 volt AC power reversed, poor grounding or system voltage too low”	“115 volt AC power reversed, ignitor (Triac) fault, poor grounding or system voltage too low”	“LINE REVERSE POLARITY”	“Reversed polarity, or Igniter (Triac) Fault / Ground fault”
9	“Ignitor Relay Fault”	“Open Inducer Limit switch”	“OPEN INDUCER LIMIT ERROR”	no 9-flash row
10	no 10-flash row	“Inducer communication error”	no 10-flash row	“Communication Error”

Replacement controls change the table again. Trane’s igniter conversion kits replace the furnace’s control, and each kit guide prints its own code table (18-CH111D1-1A-EN, pp. 1–2). Kit 20350 lists *UX2 and *DX2 models; its table gives 9 flashes as “IGNITER RELAY FAULT” (18-CH111D1-1A-EN, p. 2), where the furnace’s own guide says “Open Inducer Limit switch” (18-CD19D8-20, p. 37). The kit guides ask the installer to sign a label and attach it to the front of the blower door (18-CH111D1-1A-EN, p. 2). They do not show what the label says.

Retry counts differ too. Before the one hour lockout, the S8 and S9 tables allow 3 tries, the S8V2-C table 7 (its own flow chart says 6), the L8V1 table 5 retries, 6 in all, and the chart in the S9V2 Link kit guide 6 (S8XB-SVX001-1D-EN, p. 58; FNR-SVX002B-EN, p. 98; FNR-SVX003A-EN, pp. 59, 64; FNR-SVX007A-EN, p. 43; FNR-SVN001A-EN, p. 48). The communicating tables lock out for 1 hour after 3 ignition attempts in a row or 10 recycles in one call for heat (18-CD30D1-21-EN, p. 55).

Finding the series from the model number

Find the model number. The owner’s information has a place to record it, with the serial number (32-5083-1C-EN, p. 4). It does not say where the numbers are printed on the furnace.
Match the start of the model number to a series. Installer’s guides list the model numbers on the cover. The older ones print the first letter as an asterisk, with the note that the first letter may be “A” or “T” (18-CD29D1-18-EN, p. 1), so *UH1 stands for models starting AUH1 or TUH1. S-Series model numbers start with the series itself, for example S8X2A040M3PSC (S8XB-SVX001-1D-EN, p. 1).
Use the rows for that series. Each row in the table names its document and page, and the document list on this page gives each revision.
If your series is not in the table, these pages cannot tell you what your code means.

A series written with -H, such as *UH1-H, is the table’s label for the models with an H right after the 9 in the model number, for example *UH1B040A9H21B (18-CD33D1-11-EN, p. 1) or *UD1D140G9H51A (18-CD21D1-15-EN, p. 1). They have their own guides and tables.

What the documents say about American Standard: they treat the two brands together, and the kit guides list the same model numbers with both first letters, for example AUX2B060A9362AB and TUX2B060A9362AB (18-CH111D1-1A-EN, p. 2). They do not say which letter belongs to which brand. Two 2011 guides printed with the American Standard Heating & Air Conditioning copyright list models starting with C: CUX1 and CDX1, CUB1 and CDB1 (41-5016-12, p. 1; 41-5010-25, p. 1). American Standard line names such as Freedom, Gold, Silver or Platinum do not appear in the documents, so these pages cannot match them to a series.

Trane’s product data sheets print a line name for some prefixes. Where their covers list the same model numbers as an installer’s guide, the names are:

Prefix	Trane line name	Product data	Code list
UD1, DD1	XR 80	22-1640-15, 22-1671-15 (cover)	18-CD19D7-29-EN, p. 22
UD1, DD1 with H after the 9	XT 80	22-1779-10 (cover)	18-CD21D1-15-EN, p. 24
UE1, DE1	XB 80	22-1666-09, 22-1677-08 (cover)	18-CD19D4-28-EN, p. 21
UC1, DC1	XB 90	22-1669-15, 22-1670-10 (cover)	18-CD19D5-35-EN, p. 40
UX1, DX1	XR 90	22-1674-10 (cover)	18-CD19D6-34, p. 39
UX2, DX2	XL 90	22-1705-08 (cover)	18-CD19D8-20, p. 37
*UX2 ending AFV3VA	XV90i	22-1803-05 (cover)	18-CD25D1-6, p. 41
*UD2 ending AFV32A	XV80i	22-1802-03 (cover)	18-CD24D1-6, p. 28
UH1, DH1	XR 95	22-1836-12 (cover)	18-CD29D1-18-EN, p. 40
UH1, DH1 with H after the 9	XT 95	22-1859-07 (cover)	18-CD33D1-11-EN, p. 39
UH2, DH2	XV 95	22-1814-13 (cover)	18-CD26D1-23-EN, p. 44
UH3, DH3	XC 95	22-1806-04 (cover)	18-CD23D1-9, p. 51
UHM, DHM	XC95m	22-8301-39, pp. 5, 14	18-CD30D1-21-EN, p. 55

For the XV 80, the product data lists TUD2 and TDD2 models ending in A9V3VA or A9V3VB (22-1650-18A-EN, cover), but these pages found no installer’s guide for those models. A search of Trane’s public document library for the name XL 80 returned nothing (October 21, 2026).

Three replacement boards, CNT04829 (three stage), CNT05141 (two stage) and CNT05457 (modulating), have guides that list no furnace models (18-CH42D1-2, p. 1; 18-CH46D1-2, p. 1; 18-CH50D1-2, p. 1). The table lists them by board number.

Codes such as EP1, EP5, EP7, 7P1, 126.00 or 184.08, and 11 or 12 flashes, show up in search suggestions (Google autocomplete, checked October 21, 2026). None of them is printed as a furnace code in the Trane documents used for these pages.

What the owner’s information allows

The owner’s information 32-5083-1C-EN covers Trane and American Standard gas heating systems as a group and has no codes. It says the system requires maintenance and repair by a properly trained service technician, and that apart from the simple maintenance it describes you should not attempt any adjustments or repairs (32-5083-1C-EN, p. 3). Never remove a panel while the unit is operating; during installation and servicing the electrical supply must be disconnected and the main gas valve turned off (32-5083-1C-EN, p. 3). The unit may have a blower door switch that cuts power to the blower and gas valve when the door is removed, and the unit must not be altered to run with the door off (32-5083-1C-EN, p. 2). The furnace has automatic ignition: do not try to light it by hand, and do not touch the igniter, which is extremely hot (32-5083-1C-EN, p. 2).

The maintenance it leaves to you is the filter, cleaning the cabinet finish and keeping flammable materials away from the furnace (32-5083-1C-EN, p. 3). Where disposable filters are used, replace them every month with the same size as originally supplied, and clean or replace the filter twice a month in seasons when the unit runs more often; the arrows point in the direction of the airflow. Ask your dealer where the filter is in your system and how to service it, and never run the furnace with the filters removed (32-5083-1C-EN, p. 3). A qualified service agency should inspect the system at the start of each heating season (32-5083-1C-EN, p. 2).

Owner checks before a service call

The troubleshooting table goes by symptom and does not mention codes. In its order (32-5083-1C-EN, p. 3):

If there is no heat and the blower does not run, the table lists seven troubles with their remedies: thermostat set incorrectly, adjust it as in the operating instructions; blown fuse or tripped circuit breaker, “Replace or reset protective device or call for servicer”; defective component, “Most controls are automatic and will recycle. If your unit still does not operate call for servicer.”; burner does not ignite, call a servicer; main gas line turned off, have the gas company check; blower door removed or ajar, close it securely to restore power to the blower and gas valve; lockout, “Turn power on-off-on-off twice in 30 seconds.” (32-5083-1C-EN, p. 3).
If the heat is not enough and the blower runs all the time, clean or replace dirty air filters, and make sure the supply and return registers are open with nothing blocking the air (32-5083-1C-EN, p. 3).
If there is no heat while the vent motor runs, a restricted or plugged condensate drain is for a servicer; for a restricted or plugged venting system, make sure the vent terminals are not blocked (32-5083-1C-EN, p. 3).
For an unusual noise, call your local servicer (32-5083-1C-EN, p. 3).

The table does not say which fuse it means. On several S-Series furnaces the fuse behind code E12 is the 5 amp fuse on the control board; see E12.

Turning off the gas to the furnace

If the furnace will not operate, the start-up section says to turn off the gas to the unit and call your service technician or gas supplier (32-5083-1C-EN, p. 2). The steps (32-5083-1C-EN, p. 3):

Set the thermostat to its lowest setting.
Turn off all electric power to the unit.
Remove the front panel to reach the main gas valve.
Move the gas valve’s toggle switch to OFF.
Replace the panel.

If the furnace overheats or the gas supply fails to shut off, shut off the manual gas valve to the furnace before the electrical supply. The manual asks you to have your installer or servicer show you where that valve is (32-5083-1C-EN, p. 2).

Clearing a code

The owner’s information gives one reset, for a lockout: “Turn power on-off-on-off twice in 30 seconds.” (32-5083-1C-EN, p. 3). It does not mention codes, so these pages give that reset only on the pages for lockout codes, such as 2 flashes and E2.1.

The installer’s guides describe resets in other words, and they differ by series. On the *UX2/*DX2, a lockout must be reset by hand, by turning the system power off for more than 1 second, removing 24VAC from the control for more than 1 second, or removing the thermostat call for heat for more than 1 second but less than 20 seconds (18-CD19D8-20, p. 36). On the *UH3/*DH3 and *UHM/*DHM, the system can be reset by turning the system power off (18-CD23D1-9, p. 49; 18-CD30D1-21-EN, p. 53). The CNT05141 board guide resets a lockout by opening the door switch for at least fifteen seconds, and the control resets itself after one hour in lockout (18-CH46D1-2, p. 3). The S8 and S9 tables describe their lockouts as one hour long (FNR-SVX002B-EN, p. 98).

Two-LED controls keep the last four faults, and controls with an L6F menu the last six. Erasing these lists is an installer procedure at the thermostat terminals or the control’s buttons (18-CD19D8-20, p. 37; 18-CE04D1-1D-EN, p. 59), and these pages do not repeat it.

If a code comes back after a reset, the owner’s table sends you to a servicer: “If your unit still does not operate call for servicer.” (32-5083-1C-EN, p. 3). The owner’s information gives no step for a code that keeps returning; these pages treat it as a reason to call a technician.

When to stop and call a professional

The owner’s information says installation and service must be performed by a qualified installer, service agency or the gas supplier (32-5083-1C-EN, p. 1). Stop and call when:

You smell gas. The steps at the top of every code page are from the cover of the owner’s information (32-5083-1C-EN, p. 1). The same page says not to rely on smell alone to detect leaks and recommends U.L. recognized fuel gas and CO detectors. Propane is heavier than air and its odorant can fade, so for a furnace in a basement, an excavated area or a confined space it strongly recommends having a gas supplier install a gas detecting warning device (32-5083-1C-EN, p. 1).
The furnace overheats or the gas supply fails to shut off. Shut off the manual gas valve to the furnace before the electrical supply (32-5083-1C-EN, p. 2).
Any part of the furnace has been under water. Do not use it; a qualified service agency should inspect it and replace the gas controls, control system parts and electrical parts that have been wet (32-5083-1C-EN, p. 1).
You suspect the furnace is cycling on its limit control. The manual says to contact a qualified service technician immediately (32-5083-1C-EN, p. 2).
A flame rollout control has opened, or a pressure switch has stopped the furnace because combustion products are not exhausted properly. In both cases the manual says the cause must be investigated by a qualified service technician (32-5083-1C-EN, p. 2).
The burner does not ignite, the condensate drain is plugged, or the furnace makes an unusual noise (32-5083-1C-EN, p. 3).
The furnace still will not operate after the owner checks (32-5083-1C-EN, pp. 2–3).
The work goes beyond the filter and the owner checks: the manual says not to attempt any other adjustments or repairs (32-5083-1C-EN, p. 3).
A code keeps coming back. This is the advice of these pages; the owner’s information gives no step for codes.

Carbon monoxide: the manual’s warning is at the top of every code page (32-5083-1C-EN, p. 3). On the same page it asks you to check that all openings in the outside wall around the vent and air intake pipes are sealed, and that the furnace vent and air intake terminals are not obstructed in any way during all seasons. It quotes the U.S. Consumer Product Safety Commission’s recommendation to install carbon monoxide detectors as well as fire and smoke detectors (32-5083-1C-EN, p. 1).

Sources

52 documents

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Trane Technologies. Upflow/Horizontal and Dedicated Downflow Gas-Fired, Direct/Non-Direct Vent, 2-Stage Condensing Variable Speed Furnaces with Variable Speed Draft Inducer. 18-CE19D1-1B-EN, February 2022. Accessed Oct 21, 2026.
Trane Technologies. 40" Residential Gas Furnace Operation: Model Evolution/Nomenclature, Heating Sequence of Operation, Schematics, Ignition Systems, Service/Troubleshooting (History 1977-1991). 34-4054-08, © 2004 American Standard Inc.. Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUD1A040A9241B ... (upflow/horizontal). 22-1640-15, no revision date printed (eLibrary file dated 09/01/2018). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TDD1A060A9241B ... (downflow/horizontal). 22-1671-15, no revision date printed (eLibrary file dated 09/01/2016). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUD1A040A9H21B ... TDD1B060A9H31B .... 22-1779-10, no revision date printed (eLibrary file dated 05/01/2015). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUE1A040A9241A .... 22-1666-09, no revision date printed (eLibrary file dated 05/01/2015). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TDE1A060A9361A .... 22-1677-08, no revision date printed (eLibrary file dated 05/01/2015). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUC1B040A9241A .... 22-1669-15, no revision date printed (eLibrary file dated 03/01/2017). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TDC1B040A9241A .... 22-1670-10, no revision date printed (eLibrary file dated 05/01/2015). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUX1B040A9241A ... TDX1B040A9241A .... 22-1674-10, no revision date printed (eLibrary file dated 04/01/2009). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUX2B060A9362A ... TDX2B060A9362A .... 22-1705-08, no revision date printed (eLibrary file dated 12/01/2011). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUX2B060AFV3VA .... 22-1803-05, no revision date printed (eLibrary file dated 04/01/2009). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUD2B060AFV32A .... 22-1802-03, no revision date printed (eLibrary file dated 04/01/2009). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUH1B040A9241C ... TDH1B040A9241C .... 22-1836-12, no revision date printed (eLibrary file dated 03/01/2017). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUH1B040A9H21B ... TDH1B040A9H21B .... 22-1859-07, no revision date printed (eLibrary file dated 02/01/2018). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUH2B060A9V3VB .... 22-1814-13, no revision date printed (eLibrary file dated 03/01/2017). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUH3B060ACV3VA ... TDH3B060ACV3VA .... 22-1806-04, no revision date printed (eLibrary file dated 04/01/2009). Accessed Oct 21, 2026.
Trane Technologies. Product Data, TUD2B060A9V3VB .... 22-1650-18A-EN, May 2020. Accessed Oct 21, 2026.
Trane Technologies. Product Data / Product Handbook. 22-8301-39, Effective 1/1/26. Accessed Oct 21, 2026.
Trane Technologies. KIT 18110: 80 Volt Igniter Conversion to 120 Volt Igniter (replaces White-Rodgers 50A65-475/-476/-477). 18-CH93D1-1A-EN, 06 Jul 2020. Accessed Oct 21, 2026.
Trane Technologies. KIT 20350: SiNi 80 Volt Igniter Conversion to SiNi 120 Volt Igniter (replaces White-Rodgers 50V60-507-01, CNT08012). 18-CH111D1-1A-EN, 22 Dec 2023. Accessed Oct 21, 2026.
Trane Technologies. KIT 17399: 80 Volt Igniter Conversion to 120 Volt Igniter (replaces White-Rodgers 50C68 IFC, CNT05141). 18-CH76D1-1A-EN, 06 Jul 2020. Accessed Oct 21, 2026.
Trane Technologies. KIT 18109: SiNi 80 Volt Igniter Conversion to SiNi 120 Volt Igniter (replaces White-Rodgers 50A65-480, CNT03604). 18-CH92D1-1A-EN, 06 Jul 2020. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal, Downflow/Horizontal Gas-Fired, Direct Vent Condensing furnaces. 18-CD29D1-18-EN, 02/19. Accessed Oct 21, 2026.
Trane Technologies. High Efficiency Single Stage Upflow/Horizontal and Downflow/Horizontal Gas-Fired, Direct Vent Condensing furnaces. 18-CD33D1-11-EN, 02/19. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Downflow/Horizontal Gas-Fired Condensing furnaces. 18-CD19D5-35-EN, 02/19. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Downflow/Horizontal Gas-Fired, Direct Vent Condensing Furnaces. 18-CD19D6-34, 01/09. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal - Downflow/Horizontal, Gas-Fired Furnaces, "Fan Assisted Combustion System". 18-CD19D7-29-EN, 09/16. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal, Gas-Fired, Direct Vent, 2-Stage Condensing Furnaces with Variable Speed Inducer and Whole House Air Cleaner. 18-CD25D1-6, 12/11. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal & Downflow/Horizontal, Gas-Fired, Direct Vent, 2-Stage Condensing Furnaces with Variable Speed Inducer. 18-CD19D8-20, 12/11. Accessed Oct 21, 2026.
Trane Technologies. Variable Speed, 2-Stage, 80% Upflow/Horizontal Gas-Fired Furnaces, "Fan Assisted Combustion System" with Whole House Air Cleaner. 18-CD24D1-6, 02/11. Accessed Oct 21, 2026.
Trane Technologies. High Efficiency Single Stage Upflow/Horizontal and Downflow/Horizontal Gas-Fired Furnaces, "Fan Assisted Combustion System". 18-CD21D1-15-EN, 04/15. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal - Downflow/Horizontal, Gas-Fired Furnaces, "Fan Assisted Combustion System". 18-CD19D4-28-EN, no revision date printed (eLibrary file dated 05/01/2015). Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Downflow/Horizontal, Single Stage Direct Vent Gas-Fired Condensing Furnaces. 41-5016-12, no revision date printed (eLibrary file dated 03/01/2011). Accessed Oct 21, 2026.
Trane Technologies. Upflow Only and Downflow/Horizontal, Gas-Fired Furnaces "Fan Assisted Combustion System". 41-5010-25, no revision date printed (eLibrary file dated 03/01/2011). Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Downflow/Horizontal, Gas-Fired, Direct Vent, Variable Speed Inducer, Modulating Condensing Communicating furnaces. 18-CD30D1-21-EN, no revision date printed (eLibrary file dated September 2023). Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Downflow/Horizontal, Gas-Fired, Direct Vent, Variable Speed Inducer, 3-Stage Condensing Communicating Furnaces. 18-CD23D1-9, 02/11. Accessed Oct 21, 2026.
Trane Technologies. CNT04829 Three Stage Integrated Furnace Control for Furnaces with Variable Speed Fan. 18-CH42D1-2, 08/09. Accessed Oct 21, 2026.
Trane Technologies. CNT05141 Two Stage Integrated Furnace Control for Furnaces with Variable Speed Fan. 18-CH46D1-2, 08/09. Accessed Oct 21, 2026.
Trane Technologies. CNT05457 Modulating Integrated Furnace Control for Furnaces with Variable Speed Fan. 18-CH50D1-2, 08/09. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Downflow/Horizontal, Gas-Fired, Direct Vent, 2-Stage Condensing Furnaces with Variable Speed Inducer. 18-CD26D1-23-EN, 02/19. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Dedicated Downflow Gas-Fired, Direct/Non-Direct Vent, Single Stage / Two Stage Condensing Furnaces with High Efficiency Motor. FNR-SVX002B-EN, August 2026. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Downflow/Horizontal Gas-Fired, 1-Stage and 2-Stage Induced Draft Furnaces with High Efficiency Motor. S8XB-SVX001-1D-EN, August 2024. Accessed Oct 21, 2026.
Trane Technologies. Link Communicating or 24 Volt Gas-Fired 2 Stage Induced Draft Furnaces with Variable Speed Motor. FNR-SVX003A-EN, October 2025. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal Left/Right Gas-Fired, Single Stage Induced Draft Furnace with Variable Speed Blower Motor (natural gas only). FNR-SVX007A-EN, April 2026. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Horizontal and Dedicated Downflow Gas-Fired, Direct/Non-Direct Vent, Modulating Condensing Variable Speed Furnaces with Variable Speed Draft Inducer. FNR-SVX006B-EN, October 2026. Accessed Oct 21, 2026.
Trane Technologies. BACS9V2CA22MUAA kit: converts an S9V2-VS revision B or later furnace to a Link Communicating furnace (S9V2-VC). FNR-SVN001A-EN, October 2025. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Downflow/Horizontal Left/Right Gas-Fired, Single Stage Induced Draft Furnaces with High Efficiency Motor. 18-CE09D1-1E-EN, May 2020. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Downflow/Horizontal Gas-Fired, 1-Stage and 2-Stage Induced Draft Furnaces with High Efficiency Motor. 18-CE14D1-1A-EN, March 2020. Accessed Oct 21, 2026.
Trane Technologies. Upflow/Downflow/Horizontal Gas-Fired, 1-Stage and 2-Stage Induced Draft Furnaces with High Efficiency Motor. 18-CE04D1-1D-EN, May 2020. Accessed Oct 21, 2026.

Codes with step-by-step checks

All Trane and American Standard codes

What to check, code by code

Trane and American Standard furnace 2 flashes: system lockout

What it means

Check these first

When to call a licensed technician

Notes for different models

Trane and American Standard furnace 3 flashes: draft or pressure switch

What it means

Check these first

When to call a licensed technician

Notes for different models

Trane and American Standard furnace 4 flashes: limit or rollout open

What it means

Check these first

When to call a licensed technician

Notes for different models

Trane and American Standard furnace 9 flashes: igniter relay or inducer limit

What it means

Check these first

When to call a licensed technician

Notes for different models

Trane and American Standard furnace E2.1: retries exceeded, lockout

What it means

Check these first

When to call a licensed technician

Notes for different models

Trane and American Standard furnace E3.1: shorted pressure switch

What it means

Check these first

When to call a licensed technician

Notes for different models

Trane and American Standard furnace error code E04: open limit

What it means

Check these first

When to call a licensed technician

Notes for different models

How to read a Trane or American Standard furnace code

One LED that counts flashes

Red and green LEDs

Communicating furnaces: flash counts and alert codes

S-Series and L8V1: the seven-segment display

What the table leaves out

Why a flash count needs the series

Finding the series from the model number

What the owner’s information allows

Owner checks before a service call

Turning off the gas to the furnace

Clearing a code

When to stop and call a professional

See also

Sources