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 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. Requires professional diagnosis.
5 flashes
Flame sensed when gas valve off
Possible faulty gas valve or control board. Requires professional diagnosis.
6 flashes
Line voltage polarity incorrect
Possible wiring, transformer, or control board failure. Requires professional diagnosis.
7 flashes
Gas valve circuit problem
Possible faulty gas valve or control board. Requires professional diagnosis.
On this page:
Furnace repairs should only be performed by a certified technician.
This website is for informational purposes only. Advanpro Ltd. is not liable for property damage, personal injury, or death caused directly or indirectly by actions taken as a result of the information provided here.