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

When a gas furnace stops on a fault, its control board blinks a code on a light you see through a small window in the blower compartment door or panel (Carrier OM9GFRC-02, p. 11; Goodman HIG-2002A, p. 8; York 6100761-UUM-C-1124, p. 11). The count has no fixed meaning: three flashes is a pressure switch that did not close on a Goodman GMES9 (Goodman IOG-2020J, p. 40) but a burner that failed to light on a Lennox ML180UHV (Lennox 507945-02, p. 26), and three blinks on a Rheem RGPN is an open limit circuit (Rheem 92-24161-38-12, p. 39). A Carrier board blinks two-digit codes in short and long flashes, so three short and one long make code 31, a pressure switch fault (Carrier 59SC5A-13SI, pp. 67, 73). Below is the heating cycle as each brand’s manual prints it and the part that confirms each step. For two boards the steps are set beside the codes whose table rows name the same failure; the manuals themselves do not tie a code to a step.

The heating cycle, step by step

The installation manuals of all six brands describe one chain of steps, with different detail and different times; the last section lists the steps a manual leaves out:

1. Call for heat. The thermostat closes R to W, and the board receives 24 VAC on its W terminal (Goodman IOG-2037D, p. 36; Trane S8XB-SVX001-1D-EN, p. 78).
2. Self-check. Most of these manuals describe a self-check before the inducer starts, and they name different switches: the pressure switch open, the limits closed, or both. Trane’s S8X1 checks the flame roll-out switches, the main thermal limit and any reverse air flow switches (Trane S8XB-SVX001-1D-EN, p. 78); Carrier’s 59SC5A names only its two pressure switches (Carrier 59SC5A-13SI, p. 81). On a Lennox ML180UHV the rollout switches must be closed before 24 V reaches the thermostat at all (Lennox 507945-02, p. 24).
3. Inducer and pressure switch. The inducer fan starts, and a pressure switch closes once the fan moves enough air: “Combustion air pressure switch proves blower operation.” (Lennox 507945-02, p. 30).
4. Prepurge. The inducer runs for a set time before ignition; some documents print no prepurge, or zero.
5. Igniter. Every board here except Rheem’s heats an igniter before the gas valve opens; Carrier’s 80% owner’s manual says “When hot, the igniter will have an orange glow.” (Carrier 80GSFRN-C-03OM, p. 5). Rheem’s RGPN, 801T and 92T use a spark igniter with no warm-up (Rheem 92-24161-38-12, p. 30; Rheem 92-24161-144-09, p. 38).
6. Gas valve and flame proof. The gas valve opens, and a flame sensor must prove flame within a set time. Goodman: “Gas valve will remain open only if flame is detected.” (Goodman IOG-2020J, p. 36). No flame means a retry and, after the last one, a lockout.
7. Blower on. The house blower starts after a delay, counted from the gas valve on Carrier and York, and from ignition or flame on Lennox, Rheem and Trane’s *UX1 (table below).
8. Run. “Furnace runs, integrated control module monitors safety circuits continuously.” (Goodman IOG-2020J, p. 36).
9. End of the call. The thermostat opens R to W, the gas valve closes, the inducer runs a post-purge, and the house blower runs on for its off delay (Carrier 59SC5A-13SI, p. 81).

Times as printed

Each row follows the documents named in it. “Not stated” means the document gives no number for that step.

Series (document)	Prepurge	Igniter warm-up	Gas valve open, flame proof	Blower on	Post-purge	Blower off
Carrier 59SC5A and 58SC0A/58SC1A (Carrier 59SC5A-13SI, p. 81; Carrier 58SC0A-05SI, pp. 34, 35)	15 sec	17 sec	2-sec flame proving, starting 5 sec after the gas valve relay closes	25 sec after the gas valve	15 sec; 58SC0A: 5 seconds	90, 120, 150 or 180 sec; factory 120 on both
Carrier 59TP6C, low heat (Carrier 59TP6C-01SI, pp. 71, 72)	15 seconds	17 seconds	Same as 59SC5A	45 seconds after the gas valve (25 on high heat)	15 seconds	90, 120, 150 or 180 seconds; factory 120
Goodman GMES9 (Goodman IOG-2020J, p. 36)	15 seconds	Not stated	Not stated	30 seconds	15 seconds	100 or 150 seconds; factory 150
Goodman GR9S96, GR9S80 (Goodman IOG-2037D, p. 36; Goodman IOG-2035D, p. 19)	Not stated	Not stated	Not stated	30 seconds	15 seconds	30 to 180 seconds; default 90
Lennox ML180UHV (Lennox 507945-02, pp. 24, 30)	15 seconds	20 seconds	4-second trial for ignition	30 seconds after flame is sensed	5 seconds	“a selected OFF time delay”
Lennox ML196UHE, ML196UHEK (Lennox 507966-04, pp. 44, 47, 48; Lennox 508569-01, pp. 41, 53)	15 seconds	20 seconds	4-second trial for ignition	30 seconds (ML196UHE control 107163-01, and ML196UHEK)	Not stated	ML196UHE: factory 90 seconds; ML196UHEK: factory 120 seconds, settings 90, 120, 180 or 210
Rheem RGPN, RGPS, RGLN, RGLS (Rheem 92-24161-38-12, pp. 30, 39)	Spark 30 seconds after the pressure switch closes	None: spark ignition	“8 second trial for ignition” in the text, gas valve voltage “for only 7 seconds” in the flowchart footnote; flame proved for one second	20 seconds after the burners ignite	10 seconds	Set on the control board
Rheem 801T, 92T (Rheem 92-24161-144-09, pp. 38, 41; Rheem 92-24161-154-03, p. 86)	30 seconds	None: spark ignition	8-second trial; flame proved for one second, 8 seconds after the valve opens	Approximately 20 seconds after the burners ignite	10 seconds	801T: 90, 120, 160 or 180 seconds; factory 90
Trane *UX1, *DX1 (Trane 18-CD19D6-34, p. 36)	Not stated	Approximately 20 seconds	Within a 4 second trial period	45 seconds after ignition	Not stated	60, 100, 140 or 180 seconds; factory 100
Trane S8X1, S9X1 (Trane S8XB-SVX001-1D-EN, pp. 18, 78; Trane FNR-SVX002B-EN, pp. 23, 115)	Diagram: 0 SEC.	Text: approximately 17 seconds; diagram: 20 SEC.	Text: within 4 seconds; diagram: TFI 5 SEC.	Diagram: UP TO 30 SEC. (S8X1), 30 SEC. (S9X1)	Text: approximately 5 seconds; diagram: 5 SEC.	Set in the control menu
York Y81E, Y91E (York 6100757-UIM-C-1124, p. 55; York 6125049-UIM-C-0624, p. 48)	None before the first try; 15 s before a retry	17 s; 27 s on a retry	Flame within 7 s of the gas valve opening	30 s after the gas valve opens	15 s	Y91E: 60, 90, 120 or 180 s; factory 120

Some documents print two numbers for one step: in Trane’s S8X1 and S9X1 manuals the Sequence of Operation (“Text” above) and the timing box on the wiring diagram (“Diagram”) disagree. Carrier’s owner’s manuals print other figures than its installation manuals: an igniter heated “for about 20 seconds” and a blower delay “of up to 60 seconds” on condensing furnaces (Carrier OM9GFRC-02, p. 6), and a blower delay of “approximately 25-45 seconds” on 80% furnaces (Carrier 80GSFRN-C-03OM, p. 5). The 80% owner’s manual’s “about 17 seconds” for the igniter agrees with the 17 seconds of the installation manual.

The cycle and its codes on two boards

The strips below show a Carrier condensing furnace and a Lennox 80% furnace. A yellow box is a code from that board’s own table, placed at the step whose wording it matches; the manuals do not assign codes to steps.

1. Thermostat calls for heat: R-to-W closes

2. Self-check: pressure switches LPS and HPS open

   Pressure switch did not open: code 23

3. Inducer motor starts

4. Collector box pressure switch LPS closes; 15-sec prepurge

   Did not close or reopened: code 31

5. Hot surface igniter, 17-sec warm-up

6. 1. Gas valve opens; the igniter lights the burners

   2. Flame sensor: 2-sec flame proving, from 5 sec after the gas valve relay closes

   Flame not proved, code 34: up to three more Trials-For-Ignition

   1. Ignition lockout: code 14

   2. Resets after three hours

7. Flame proved: blower on 25 sec after the gas valve is energized

8. Thermostat satisfied: gas valve closes

   Flame proved with the valve de-energized: code 22

9. Inducer 15-sec post-purge

10. Blower runs 90 to 180 sec, factory 120

The manual does not say whether the igniter warm-up repeats on a retry. Code 33, a limit or flame rollout switch open, is not tied to one step on the label. Open longer than 3 minutes, it becomes lockout 13.

1. Rollout switches closed: 24 V reaches the thermostat

   Rollout switch open: 8 flashes

2. Thermostat calls for heat; self-check: primary and secondary limits closed

   Limit open: 7 flashes

3. Combustion air inducer starts

   Pressure switch stuck closed before the inducer starts: 11 flashes

4. Combustion air pressure switch closes

   Failed to close or opened during heat demand: 9 flashes

5. 1. 15-second pre-purge

   2. Hot surface ignitor, 20-second warm-up

   3. Gas valve opens: 4-second trial for ignition

   Burner failed to light, or lost flame during heat demand, 3 flashes: repeated four more times

   1. Watchguard: 5 flashes

   2. Restarts after 60 minutes, or thermostat Heat, OFF, Heat

6. Flame sensed; blower on 30 seconds later

7. Heat demand satisfied: gas valve de-energized

   Flame sensed without gas valve energized: 12 flashes

8. Inducer 5-second post-purge

9. Blower runs its selected off delay

Reading the light on each board

The owner’s manuals put the light behind a window in the blower door or panel: the “view port in the blower access panel” on Carrier condensing furnaces (Carrier OM9GFRC-02, p. 11), the “blower compartment sight glass” on Goodman (Goodman HIG-2002A, p. 8), the “viewport on the lower access panel” on Lennox, in the owner’s manual for the EL180UHNE (Lennox 507648-02, p. 3) and a “clear view port in the blower compartment door” on York (York 6100761-UUM-C-1124, p. 11). Carrier’s 80% owner’s manual does not mention the light, and the Rheem and Trane owner’s manuals used here describe no flash codes.

Read the code before you open anything. Carrier’s condensing owner’s manual is the only one in this set that says so: “Record the LED status code BEFORE removing the blower access door or turning off 115-v power to the furnace.” (Carrier OM9GFRC-02, p. 10). On Goodman, Trane and York furnaces opening the door stops the furnace or cuts its power. Trane’s *UX1 guide describes a “blower door switch which cuts power to the blower and gas valve” (Trane 18-CD19D6-34, p. 36). Goodman: “An interlock switch prevents furnace operation if the blower door is not in place.” (Goodman HIG-2002A, p. 6). York: “Removing this panel or door cuts off the electric power supply.” (York 6100761-UUM-C-1124, p. 11). On a Goodman GMES9 the “LED Flash code will cease if power to the control module is interrupted through the disconnect or door switch” (Goodman IOG-2020J, p. 40).

Board	What a code looks like	Normal operation	Code memory
Carrier 59SC5A, 58SC0A, amber LED (Carrier 59SC5A-13SI, pp. 67, 73, 81; Carrier 58SC0A-05SI, pp. 31, 37)	Two digits: “The first digit is the number of short flashes, the second digit is the number of long flashes.” Rapid flashing: line voltage polarity reversed	On continuously; code 12 during the 90-sec blower period after power returns during a call for heat	Kept when power is interrupted, though the 58SC0A manual says red-LED boards also erase stored codes when power is lost; on the 59SC5A “erased automatically after 72 hours”. Recall is a technician step
Carrier 59TP6C, display and LED (Carrier 59TP6C-01SI, pp. 54, 56, 71)	Display: major code in the first two digits, minor code in the third; the LED flashes the major code	LED on continuously	FLt menu: the 7 latest faults
Goodman GMES9, red LED (Goodman IOG-2020J, p. 38)	Number of red flashes	“Continuous On Normal Operation”	Stored codes are “auto-erased after 14 days”; a button flashes the last five, newest first. Code 7 is not stored
Goodman GR9S96, GR9S80, display (Goodman IOG-2037D, pp. 42, 43)	“Err” with the code, such as EE2	“IdL”, idle, “Normal operation.”	F10 menu: the last 10 faults
Lennox ML180UHV, ML196UHE, red LED (Lennox 507945-02, p. 26; Lennox 507966-04, pp. 40, 41)	X flashes, 1/3 second on and off (ML180UHV) or ½ second (ML196UHE), then 3 seconds off	Idle: “Heartbeat”, 1 sec on, 1 sec off. Heat call: “Continuous Rapid Flash”, or on control 107163-01 a “Fast Heartbeat”, 0.5 s on, 0.5 s off	Last 5 codes (ML180UHV) or last 10 (ML196UHE), kept “including when power is shut off”
Lennox ML196UHEK, display (Lennox 508569-01, p. 44)	E-codes, such as E111	Idle: the decimal point blinks at 1 Hz	“E” menu: the most recent 10 codes
Rheem RGPN, green and amber LEDs (Rheem 92-24161-38-12, p. 39)	The green STATUS LED blinks codes 1 to 5; the amber FLAME LED shows the flame	Amber “STEADY ON = Normal Flame Sense”	Not given on the pages used here
Rheem 801T, 92T, display and amber LED (Rheem 92-24161-144-09, pp. 39, 42)	Two digits, each shown for one second, then a ½ second pause	Display “0” in standby, “H” with gas heat on; the amber flame LED on continuously	Faults clear after one week; at a power reset the three most recent flash in turn
Trane *UX1, *DX1, one LED (Trane 18-CD19D6-34, p. 39)	Number of flashes	“Flashing Slow” with no call for heat, “Flashing Fast” with a call for heat	The guide describes no code memory
Trane S8X1, S9X1, display (Trane S8XB-SVX001-1D-EN, pp. 52, 61, 78; Trane FNR-SVX002B-EN, pp. 99, 115)	Codes such as E2.1 and E04	“IDL” with no thermostat demand	“Last 6 Faults” menu, L6F
York Y81E, Y91E, red, green and amber LED (York 6100757-UIM-C-1124, pp. 57, 59; York 6125049-UIM-C-0624, pp. 49, 50)	Red flashes, 1/3 s on and 1/3 s off, repeated the number of times of the code, then a 2 s pause	Slow green flash: standby. Slow amber flash: call for heat. Slow is 2 s on, 2 s off	Up to five codes, kept when power is lost; the feature “must only be used by a qualified service technician”

1/3 s2 s

3 short1 longnot to scale

York’s owner’s manual gives the flash timing as 1/4 s on and 1/4 s off, against 1/3 s in the installation manual, and of the red codes it describes only “Rapid red flashes: There is a problem with the operation of this furnace.” (York 6100761-UUM-C-1124, p. 11; York 6100757-UIM-C-1124, p. 57). The Lennox ML196UHE manual prints tables for two ignition controls, 103217-03 and 107163-01, and does not say which one a given furnace has (Lennox 507966-04, pp. 40, 41).

Ignition attempts and lockout

When the flame sensor finds no flame, every board here tries again before it locks out. Carrier boards lock out for three hours; the other brands print one hour where they give a length.

Board	Tries before lockout	Code and lockout	What ends the lockout
Carrier 59SC5A, 58SC0A, 59TP6C (Carrier 59SC5A-13SI, pp. 67, 81; Carrier 58SC0A-05SI, pp. 34, 37; Carrier 59TP6C-01SI, pp. 56, 71)	The first trial and “up to three more Trials-For-Ignition”; the 58SC0A guide says “4 attempts”	14 (14.1 on the 59TP6C); three hours	Resets itself after three hours, or “by momentarily interrupting 115 vac power to the furnace”, or 24 vac at SEC1 or SEC2
Goodman GMES9 (Goodman IOG-2020J, p. 38; Goodman HIG-2002A, p. 6)	“three attempts during a single call for heat”	1 flash; one hour	Resets itself after one hour; 115 volt power interrupted; thermostat lowered for 1 to 20 seconds. Owner’s manual: power off more than 20 seconds, or thermostat signal off 0 to 20 seconds
Goodman GR9S96, GR9S80 (Goodman IOG-2037D, p. 43; Goodman IOG-2035D, p. 31)	Ignition “retries” (3 total)	EE0; length not stated	Not stated
Lennox ML180UHV, ML196UHE, ML196UHEK (Lennox 507945-02, pp. 26, 30; Lennox 507966-04, p. 44; Lennox 508569-01, pp. 46, 53)	The first trial, then “four more times”	5 flashes (ML180UHV, ML196UHE) and E270 (ML196UHEK); the sequence text calls the lockout “WATCHGUARD” and repeats after 60 minutes; the E270 row says “Clears when heat call finishes successfully”	Restarts after 60 minutes, or the thermostat goes from “Heat” to “OFF” and back to “Heat”
Rheem RGPN (Rheem 92-24161-38-12, pp. 30, 39)	“up to four times (first attempt followed by three retries)”	1 blink; a one-hour “soft-lockout”	Main power off for five seconds, or the heat call off and back on. The same page later says “5 to 10 seconds”, the flowchart “wait 30 seconds”
Rheem 801T, 92T (Rheem 92-24161-144-09, pp. 38, 40; Rheem 92-24161-154-03, p. 86)	Up to four times	The display alternates 10 and the fault’s code; 1 hour	Resets itself after one hour; power off and on, or the heat call off for more than 2 and less than 20 seconds
Trane *UX1, *DX1 (Trane 18-CD19D6-34, pp. 37, 39)	Not stated: the control will “recycle the ignition sequence”, then lock out	2 flashes; length not stated	Power “off, then on, then off and then on again within 30 seconds”, at the unit’s power source or at the thermostat
Trane S8X1, S9X1 (Trane S8XB-SVX001-1D-EN, p. 18; Trane FNR-SVX002B-EN, pp. 23, 98)	Diagram box: “RETRIES: 2”; S9X1 code table: “one hour lockout after 3 times”	E2.1; one hour in the S9X1 table	Diagram box: “AUTO RESTART: 60 MIN.”
York Y81E, Y91E (York 6100757-UIM-C-1124, pp. 55, 58, 59; York 6125049-UIM-C-0624, pp. 48, 49, 50)	“If three retries occur during a call for heat, the furnace shuts down for 1 h”; the 7 red flashes entry says “three trials for ignition”	7 red flashes; 1 h	Restarts after 1 h. A hard lockout, such as 5 red flashes, needs power turned off and back on

Carrier’s owner’s manuals count the same lockout two more ways: “after four attempts” (Carrier OM9GFRC-02, p. 6) and “three more ignition cycles” (Carrier 80GSFRN-C-03OM, p. 5). York boards also lock out on pressure switch trips: 6 red flashes means the switch opened four times during the call for heat on the Y81E and five times on the Y91E, followed by a 1 h lockout (York 6100757-UIM-C-1124, p. 58; York 6125049-UIM-C-0624, p. 49).

One failure, different codes

Do not carry a code from one board to another, even within one brand. Carrier’s 59SC5A shows one code, 31, for both of its pressure switches, while the two-stage 59TP6C shows 32.2 for the main switch and 31.6 for the secondary one (Carrier 59SC5A-13SI, p. 67; Carrier 59TP6C-01SI, p. 56). Use the table for your own series. Carrier’s owner’s manual points to “the information booklet inside the main furnace door for a service code legend” (Carrier OM9GFRC-02, p. 10); Goodman’s sends you to the installation instructions “for code identification” (Goodman HIG-2002A, p. 8).

How to read the table: where a cell gives two codes, the first is the brand’s LED board and the second its display board. That is Carrier 59SC5A and 58SC0A, then 59TP6C; Goodman GMES9, then GR9S96 and GR9S80; Lennox ML180UHV and ML196UHE, then ML196UHEK; Rheem RGPN, then 801T and 92T; Trane *UX1, then S8X1 and S9X1. York’s Y81E and Y91E use the same counts except where the cell says otherwise. “Not in this board’s table” means that board’s code list has no row for the failure. The pages for each brand are in the last row.

Failure	Carrier	Goodman	Lennox	Rheem	Trane	York
Pressure switch did not close	31; 32.2 for the main switch, 31.6 for the secondary	3 flashes; EE2	9 flashes; E223	2 blinks; 57	3 flashes, “Draft Pressure Error”; E3.2	3 red flashes
Pressure switch closed before the inducer starts	23; 23.4 and 23.5	2 flashes; EE1	11 flashes; E224	4 blinks; 55	Not in this board’s table (*UX1); E3.1	2 red flashes
Limit open	33, which becomes lockout 13 after 3 minutes; 33.1 and 13.1	4 flashes; EE3	7 flashes; E250	3 blinks; 22	4 flashes; E04	4 red flashes; 11 red flashes if open longer than 5 min; 5 red flashes if open longer than 15 min
Rollout switch open	The same 33 and 13 as the limit (59SC5A, 58SC0A)	6 flashes; E11	8 flashes; E200	Not in this board’s table (RGPN), though its 3-blink checklist lists rollouts; 33	Not in this board’s table (*UX1); E04, shared with the limit	5 red flashes
Ignition lockout	14, after a 34 on each failed trial; 14.1	1 flash; EE0	5 flashes; E270	1 blink; 10 with 11	2 flashes; E2.1	7 red flashes
Flame sensed with the gas valve closed	22; 22.1	5 flashes; EE4	12 flashes; E241	Rapid blink of the amber LED; 14	5 flashes; E05	1 red flash
Weak flame signal	Not in this board’s table, on all three; the checks under 34 list “.5 microamps D.C. min., 4.0 - 6.0 nominal”	7 flashes, not stored in memory; EE6	4 flashes; E240	Slow blink of the amber LED; 12	8 flashes; E08	Rapid amber flash; on the Y91E also a continuous amber flash, below 0.35 µA
Reversed polarity or poor ground	Rapid flashing; 10.1	Rapid flash for polarity, 12 flashes (“Inducer Relay Error/Improper Grounding”); EEA, and E10 for a grounding fault	1 flash for polarity, 2 for ground; E111 and E112	Not in this board’s table (RGPN); 26	6 flashes; E6.1 and E6.2	9 red flashes
Open 24 V fuse	24; 24.1	10 flashes, though the GMES9 chart on p. 41 lists a blown fuse under 6 flashes; EE5	Not in this board’s table, on all three	Not in this board’s table, on all three	Not in this board’s table (*UX1); E12	No flash count. Y81E: if the LED does not flash at all, check power and the fuse. Y91E: “An open fuse results in a steady on red LED”
Pages	Carrier 59SC5A-13SI, p. 67; Carrier 58SC0A-05SI, pp. 31, 37; Carrier 59TP6C-01SI, p. 56	Goodman IOG-2020J, pp. 38, 40, 41; Goodman IOG-2037D, pp. 43, 44; Goodman IOG-2035D, pp. 31, 32	Lennox 507945-02, p. 26; Lennox 507966-04, pp. 40, 41; Lennox 508569-01, pp. 44, 46	Rheem 92-24161-38-12, p. 39; Rheem 92-24161-144-09, pp. 39, 40; Rheem 92-24161-154-03, pp. 87, 91	Trane 18-CD19D6-34, p. 39; Trane S8XB-SVX001-1D-EN, pp. 17, 61; Trane FNR-SVX002B-EN, pp. 98, 99	York 6100757-UIM-C-1124, pp. 57, 58; York 6125049-UIM-C-0624, pp. 49, 50

Some manuals disagree with themselves. Carrier’s 59SC5A troubleshooting guide says an open limit “changes to lockout #7” and that “status code #4 continues to flash”, where the service label of the same manual prints 13 and 33; the label lists no code 7 or 4 (Carrier 59SC5A-13SI, pp. 67, 83). A note in Trane’s S8X1 sequence, written for the two-stage S8X2, says that if the pressure switch does not close “the control will report a e3.1 error”, while the error list calls E3.1 “Shorted Pressure Switch” and E3.2 “Open Pressure Switch” (Trane S8XB-SVX001-1D-EN, pp. 61, 78).

What an owner can check, and what is technician work

If you smell gas, stop here and follow the “What to do if you smell gas” instructions for your furnace; Carrier’s begin “Do not try to light any appliance.” and include “Leave the building immediately.” (Carrier OM9GFRC-02, p. 1).

The code tables on this page come mostly from installation manuals written for installers and service technicians; the owner’s manuals in this set do not decode the counts. Goodman’s tells you to “record the number of flashes seen in sequence”, shut the unit down and “contact a qualified servicer for further troubleshooting and/or repairs” (Goodman HIG-2002A, p. 8).

The checks the owner’s manuals do give you:

• Thermostat set to heat and above room temperature (Goodman HIG-2002A, p. 8; Lennox 507648-02, p. 5).
• Power to the furnace on, no tripped breaker or blown fuse in the house panel (Goodman HIG-2002A, p. 8; Lennox 507648-02, p. 5; York 6100761-UUM-C-1124, p. 10).
• Gas on: the manual shut-off valve in the gas pipe open and the on/off switch on the gas valve on (York 6100761-UUM-C-1124, p. 10). Lennox adds “Is gas turned on at meter?” (Lennox 507648-02, p. 6).
• Filter clean. Goodman calls a dirty filter “the most common cause of improper furnace operation” and asks for a check “at least once a month” (Goodman HIG-2002A, p. 8).
• Return and supply grilles open (Goodman HIG-2002A, p. 8).
• Vent and intake clear: “Check intake and vent terminations on high efficiency furnaces to make sure they are not blocked.” (Goodman HIG-2002A, p. 8). York asks for a look at the “combustion air and vent pipe for blockage or leakage” every time you change the filters (York 6100761-UUM-C-1124, p. 9). On Rheem condensing furnaces a pressure switch shuts off the burners “if the condensate drain line becomes blocked” (Rheem 92-20802-128-03, p. 8).
• Blower door closed and in place (York 6100761-UUM-C-1124, p. 11; Trane 32-5083-1C-EN, PDF p. 3).
• Lockout reset, where the owner’s manual gives one: Goodman’s power interruption or thermostat cycle (Goodman HIG-2002A, p. 6), Trane’s “Turn power on-off-on-off twice in 30 seconds.” (Trane 32-5083-1C-EN, PDF p. 3).

The same filter and vent checks, with their intervals, are on our winter checklist and in the home maintenance schedule.

If the furnace locks out again, the owner’s part ends. Goodman: “If your furnace frequently locks out, a problem exists which must be corrected. Contact a qualified servicer.” (Goodman HIG-2002A, p. 6). Carrier: “If lockout occurs, main burners fail to light, or blower does not come on, shut down the furnace and call your dealer for service.” (Carrier OM9GFRC-02, p. 6).

The rest is technician work, in the brands’ words. Carrier: “Untrained personnel can perform basic maintenance functions such as cleaning and replacing air filters. All other operations must be performed by trained service personnel.” (Carrier 59SC5A-13SI, p. 73). Lennox: “Do not attempt to service the unit in any way.” (Lennox 507648-02, p. 5). Rheem: “Routine maintenance to be provided by a qualified installer, service agency or the gas supplier ONLY.” (Rheem 92-20802-130-02, p. 7). York: “The user must not purchase, install, or replace any components of this furnace.” (York 6100761-UUM-C-1124, p. 11). Treat the checks printed under each code in the installation manuals (pressure tubing, gas valve, flame sense microamps, polarity and ground) as that technician’s work.

The rollout switch: who may reset it

Trane’s owner’s information says a Flame Rollout Protection Control opens “If flames from the burner are not properly drawn into the heat exchanger” (Trane 32-5083-1C-EN, PDF p. 2). Several brands use a manual-reset switch, and their manuals disagree on who resets it:

• Carrier, condensing owner’s manual, in its checklist for a furnace that fails to operate, after the line “NOTE: Turn off electrical supply before continuing with checklist.”: “Check manual reset rollout switch located on the burner box. […] Reset it by pushing the button on the switch. If it trips again, shut down the furnace and call for service.” (Carrier OM9GFRC-02, p. 11).
• Carrier, 80% owner’s manual, for “the manual reset limit switches located on the ends of the burner enclosure” (it does not use the word rollout): “Reset the switches by pushing the button on the switch. If the switch trips a second time, turn off the furnace and call for service.” (Carrier 80GSFRN-C-03OM, p. 7).
• Rheem RGPN installation instructions: “If a switch is tripped, it must be manually reset. DO NOT jumper or reset this switch. If this switch should trip, a qualified installer, service agency or the gas supplier should be called to diagnose and/or correct the source of tripping.” (Rheem 92-24161-38-12, p. 35).
• Trane *UX1 installer’s guide, for the “manual reset temperature limit located on the burner box” (again, no word rollout): after a check of the vent and combustion air inlet terminations, “If blockage exists, clear the problem and then the reset button may be depressed. If there is no blockage of the terminations, the limit switch must be reset by a qualified servicer.” (Trane 18-CD19D6-34, p. 37). Trane’s owner’s information: “The cause must be investigated by a qualified service technician.” (Trane 32-5083-1C-EN, PDF p. 2).
• Lennox ML180UHV installation instructions: “If flame rollout switches are tripped, call the service technician for inspection.” (Lennox 507945-02, p. 30).
• York Y81E: “The rollout control is manually reset.” The board then holds a hard lockout, and power “has to be cycled off and on to reset the control after the problem has been corrected” (York 6100757-UIM-C-1124, p. 58).

The Rheem text says in one breath that the switch “must be manually reset” and “DO NOT jumper or reset this switch”; it is clear only that a qualified installer, service agency or gas supplier finds the cause. Our advice: if your own manual gives the owner no reset step, leave the switch alone and call a qualified service technician.

Furnace codes on this site

• Carrier: 31, pressure switch; 23, pressure switch did not open; 33, limit circuit fault; 13, limit circuit lockout; 34, ignition proving failure; 14, ignition lockout; 24, secondary voltage fuse; 12, blower on after power up; all Carrier furnace codes
• Goodman: 1 flash, 2 flashes, 3 flashes, 4 flashes, 6 flashes and 7 flashes on single-LED boards; EE0, EE3 and IdL on the display; all Goodman furnace codes
• Lennox: 3 flashes; E223, pressure switch failed open; E250, limit switch circuit open; E270, soft lockout after retries; all Lennox furnace codes
• Rheem: 2 blinks and 3 blinks on RGPN boards; 57, pressure switch open; 22, main limit open; 0, standby; all Rheem furnace codes
• Trane: 2 flashes, 3 flashes, 4 flashes and 6 flashes on single-LED boards; E2.1, E3.1, E04 and E12 on the display; all Trane furnace codes
• York: 1 red flash, 2 red flashes, 3 red flashes, 4 red flashes, 5 red flashes, 6 red flashes, 7 red flashes, 8 red flashes, 11 red flashes; all York furnace codes

What these documents do not cover

• Several steps have no printed time (“Not stated” in the times table). The Lennox ML196UHE and ML196UHEK texts describe no self-check, the Rheem RGPN text no switch check at the start of a call, the York texts no self-check or prepurge before the first try.
• The Trane *UX1 guide has no code for a blown fuse or a stuck pressure switch, and describes no code memory.
• None of the owner’s manuals here gives the meaning of a flash count. The Rheem documents print no issue date.
• Of two-stage furnaces only the low-heat cycle of the Carrier 59TP6C was read. Modulating and communicating furnaces, gas pressure, carbon monoxide levels and vent rules are outside this page.
• Bryant, Payne, American Standard, Coleman and Luxaire documents were not read for this page. Every time and code above belongs to the series and revision named with it; check the label and manual of your own furnace.

See also

• Heat pump vs gas calculator
• Furnace and HVAC tax credits for 2025 and 2026: 25C ended after 2025
• Form 5695 for 2025 and 2026: QMID, lines, carryforward
• Home maintenance schedule from the manuals: monthly to yearly
• Winter home maintenance checklist: furnace, boiler, water heater
• Water heater or furnace closet: clearance and air requirements

Error codes: Carrier, Goodman, Lennox, Rheem furnaces, Trane and American Standard, York, Coleman and Luxaire