American Standard, Trane Furnace Error Codes
Look up error codes to identify furnace problems and estimate repair costs.
Locating the furnace error code
Refer to the furnace glossary if you need help identifying furnace parts or terms.
All high-efficiency furnaces and most mid-efficiency furnaces show error codes on the control board, either as a flashing LED sequence or on a display .
Where to find the control board and inspection port
The furnace control board is almost always in the lower compartment. You can view the error code LED or display through a small, clear plastic inspection port in the centre of the lower furnace cover.
If the control board isn’t in the lower compartment, it’s in the upper compartment.
How to access the inspection port
Furnaces with upper and lower furnace covers — The inspection port is usually on the lower furnace cover and is accessible without removing the cover.
Furnaces with a one-piece front cover — Remove the front cover first. The inspection port is usually on the secondary cover for the lower compartment.
If the control board is in the upper compartment — You need to remove the upper furnace cover. If there are thumb screws, loosen them and pull the cover out from the screw location. If there are no screws, slide the cover straight up, then pull it out.
Error codes
Don’t turn off the power to the furnace while troubleshooting — unless instructed otherwise. Turning off the power clears the current error code.
Observe the flashing LED sequence or display code, which may repeat in a loop. Watch it carefully, make note of the sequence or digits, and match it up with the corresponding code below:
LED off
No power. Continue to the Power diagnostic →
LED flashing slowly
Normal operation, no call for heat. Continue to the Thermostat diagnostic →
LED flashing quickly
Normal operation, furnace should be running or cycling. Continue to the Secondary diagnostic →
LED on, not flashing
Control board problem. Possible wiring problem, transformer issue, or faulty control board. Book a professional repair.
2 flashes
Lock out on retries. Continue to the Secondary diagnostic →
3 flashes
Pressure switch error. Continue to the Secondary diagnostic →
4 flashes
Open limit switch. Continue to the Secondary diagnostic →
5 flashes
Flame sensed when gas valve off. Possible faulty gas valve or control board. Book a professional repair or continue to the Gas valve diagnostic →
6 flashes
Line voltage polarity incorrect. Possible wiring, transformer, or control board failure. Book a professional repair.
7 flashes
Gas valve circuit problem. Possible faulty gas valve or control board. Book a professional repair or continue to the Gas valve diagnostic →
8 flashes
Low flame sensor. Faulty flame sensor, igniter, or gas valve. Book a professional repair or continue to the Flame sensor, Igniter, or Gas valve diagnostic →
9 flashes
Igniter problem. Faulty igniter or gas valve. Book a professional repair or continue to the Igniter diagnostic →
Error code not listed
Other furnace problem. Continue to the Secondary diagnostic →
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