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Trane and American Standard furnace code E12: open fuse

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HHW · ERROR-CODES · TRANE · E12
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Short answer On Trane and American Standard S-Series and L8V1 furnaces, E12 means an open fuse: the onboard 5 amp fuse on the S9X, S8V2-C and S9V2 Link kit, a low voltage fuse on the L8V1 and S9VM. Finding the cause is technician work. See what to check

Furnace control LED or display

E12

“Open fuse”

Technician

Printed on 8 model series · 4 documents

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

What it means

E12 means an open fuse. The S8, S9X, S8V2-C and S9V2 Link kit tables word it “Open fuse” (S8XB-SVX001-1D-EN, p. 59; FNR-SVX002B-EN, p. 99; FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 46). The troubleshooting charts for the S9X, the S8V2-C and the S9V2 Link kit say which fuse: “The onboard 5 amp fuse is open or missing.” (FNR-SVX002B-EN, p. 112; FNR-SVX003A-EN, p. 76; FNR-SVN001A-EN, p. 67). The L8V1 table calls it “Low voltage fuse blown” (FNR-SVX007A-EN, p. 43), and the S9VM table “Open Low Voltage Fuse” (FNR-SVX006B-EN, p. 106).

The two tables that give causes point to the low voltage wiring and the accessories connected to it. The L8V1 action is to verify that approved accessories are connected to the transformer power and to reconnect the low voltage field wiring, wire by wire if necessary, to find the component (FNR-SVX007A-EN, p. 43). The S9VM causes are shorted low voltage field wiring, a high amp draw in the low voltage circuit from accessories, and high resistance in the field wiring (FNR-SVX006B-EN, p. 106). These lists are for the L8V1 and the S9VM.

Check these first

The owner’s information (32-5083-1C-EN) has no code list and no step for E12. Its troubleshooting table goes by symptom and does not mention codes. The rows an owner can act on, in the table’s order:

  1. Check that the thermostat is set correctly (32-5083-1C-EN, p. 3).
  2. For a blown fuse or tripped circuit breaker: “Replace or reset protective device or call for servicer.” (32-5083-1C-EN, p. 3). See the note below the list.
  3. If the main gas line is turned off: “Have gas company check.” (32-5083-1C-EN, p. 3).
  4. 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).
  5. 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).
  6. 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. Its fuse row does not say which fuse it means. The furnace documents name the fuse behind E12: the S9X, S8V2-C and S9V2 Link kit charts call it the onboard 5 amp fuse (FNR-SVX002B-EN, p. 112; FNR-SVX003A-EN, p. 76; FNR-SVN001A-EN, p. 67), and the L8V1 and S9VM tables a low voltage fuse (FNR-SVX007A-EN, p. 43; FNR-SVX006B-EN, p. 106). The S9V2 IOM says only qualified technicians should attempt to troubleshoot or repair the appliance (FNR-SVX001C-EN, p. 83). These pages read the owner’s row as the fuses and breakers outside the furnace and treat the fuse behind E12 as technician work. The owner’s information also says that apart from the simple maintenance it describes, 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

  • Finding why the fuse opened, in the low voltage wiring and the accessories (FNR-SVX007A-EN, p. 43; FNR-SVX006B-EN, p. 106), and the onboard fuse itself (FNR-SVX002B-EN, p. 112).
  • A furnace whose LEDs show a fuse state, on the boards in the notes below.
  • E12 comes back after the fuse is replaced. The owner’s information gives no step for codes; these pages send it to the technician.

Notes for different models
Series or board Code or LED state Wording Source
S8B1, S8X1, S8X2, S9B1, S9X1, S9X2, S8V2-C, S9V2-VC (Link kit) E12 “Open fuse” S8XB-SVX001-1D-EN, p. 59; FNR-SVX002B-EN, p. 99; FNR-SVX003A-EN, p. 59; FNR-SVN001A-EN, p. 46
L8V1 E12 “Low voltage fuse blown” FNR-SVX007A-EN, p. 43
S9VM E12 “Open Low Voltage Fuse” FNR-SVX006B-EN, p. 106
Boards CNT04829, CNT05141, CNT05457 red LED off and STATUS LED off “24Vac Fuse Open” 18-CH42D1-2, p. 6; 18-CH46D1-2, p. 6; 18-CH50D1-2, p. 7
Replacement control kits green and red LEDs continuously off “FUSE OPEN” 18-CH76D1-1A-EN, p. 2; 18-CH92D1-1A-EN, p. 2; 18-CH93D1-1A-EN, p. 2; 18-CH111D1-1A-EN, p. 2
*UH2/*DH2 green and red LEDs on continuously “FUSE OPEN OR INTERNAL CONTROL FAILURE” 18-CD26D1-23-EN, p. 44
*UX2/*DX2, *UD2 solid red with solid green STATUS LED “Continuous Reset caused by a blown fuse or internal error.” 18-CD19D8-20, p. 37; 18-CD24D1-6, p. 28
*UH3/*DH3, *UHM/*DHM alert CHECK FUSE, no flash count alert code 92, “24V Fuse Open” 18-CD30D1-21-EN, p. 55

A dark LED does not always mean the fuse: on single-LED boards a light that stays off reads “Check Power” (18-CD19D5-35-EN, p. 40). The S9V2 Link kit table lists E12 with communication code ERR 092.00 (FNR-SVN001A-EN, p. 46).

Related Trane and American Standard codes

  • E01 “Loss of the IRQ or other internal failures (Internal IFC error)”
  • 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)”

See also

Other gas furnaces: Carrier, Goodman, Lennox, Rheem furnaces, York, Coleman and Luxaire

All Trane and American Standard codes

Trane and American Standard are trademarks of their owners. How House Works is not affiliated with or endorsed by Trane and American Standard.

Sources

20 documents
  1. Trane Technologies. Gas Heating Systems - Owner's Information. 32-5083-1C-EN, © 2024. Accessed Oct 21, 2026.
  2. Trane Technologies. Upflow/Horizontal and Dedicated Downflow Gas-Fired, Direct/Non-Direct Vent, 2-Stage Condensing Variable Speed Furnaces with Variable Speed Draft Inducer. FNR-SVX001C-EN, August 2026. Accessed Oct 21, 2026.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. Trane Technologies. Upflow/Horizontal and Downflow/Horizontal Gas-Fired Condensing furnaces. 18-CD19D5-35-EN, 02/19. Accessed Oct 21, 2026.
  8. 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.
  9. 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.
  10. 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.
  11. Trane Technologies. CNT04829 Three Stage Integrated Furnace Control for Furnaces with Variable Speed Fan. 18-CH42D1-2, 08/09. Accessed Oct 21, 2026.
  12. Trane Technologies. CNT05141 Two Stage Integrated Furnace Control for Furnaces with Variable Speed Fan. 18-CH46D1-2, 08/09. Accessed Oct 21, 2026.
  13. Trane Technologies. CNT05457 Modulating Integrated Furnace Control for Furnaces with Variable Speed Fan. 18-CH50D1-2, 08/09. Accessed Oct 21, 2026.
  14. 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.
  15. 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.
  16. 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.
  17. 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.
  18. 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.
  19. 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.
  20. 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.