Aire-Flo, Armstrong 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 .

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.

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 on, not flashing

Normal operation

Continue to the Secondary diagnostic

1 flash

Flame sensed with gas valve off

Faulty gas valve or control board.

2 flashes

Closed pressure switch with inducer off

Faulty pressure switch.

3 flashes

Open pressure switch with inducer on

Continue to the Secondary diagnostic

4 flashes

Primary limit switch open

Continue to the Secondary diagnostic

5 flashes

Rollout switch open

Cracked primary heat exchanger or plugged secondary heat exchanger. Professional diagnosis required.

6 flashes

Pressure switch cycle lockout

Continue to the Secondary diagnostic

7 flashes

Lockout, burners fail to light

Continue to the Secondary diagnostic

8 flashes

Lockout, burners lost flame too many times

Continue to the Secondary diagnostic

9 flashes

Line voltage polarity incorrect

Possible wiring, transformer, or control board failure. Professional diagnosis required.

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Furnace repairs should only be performed by a certified technician.

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