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Common 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 look it up in your furnace manual or manufacturer’s website. 

Find the matching description below to continue troubleshooting and estimate repair costs:

No power

Continue to the Power diagnostic

Normal operation

Continue to the Secondary diagnostic

Abnormal or weak flame sensor signal

Faulty flame sensor, igniter, or gas valve.

Circuit board failure or control wired incorrectly

Possible faulty wiring or control board.

Flame sensed with gas valve off

Possible faulty gas valve or control board. Professional diagnosis required

Gas heating lock out

Continue to the Secondary diagnostic

Gas valve circuit error

Faulty gas valve or control board.

Ignition lock out

Continue to the Secondary diagnostic

Ignition proving error

Continue to the Secondary diagnostic

Igniter fault

Faulty wiring or igniter.

Improper main ground or less than 75 volts

Professional diagnosis required.

Limit or flame roll out switch open

Continue to the Secondary diagnostic

Pressure switch closed when inducer off

Faulty pressure switch or control board.

Pressure switch did not close

Continue to the Secondary diagnostic

Pressure switch did not open (primary or secondary)

Faulty pressure switch, inducer motor, or blocked intake/exhaust.

Secondary voltage fuse

Fuse blown on low voltage circuit

Possible faulty wiring or control board.

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.

Repair Wiring or Igniter

$199 or $379 + GST

Mention this diagnosis from the troubleshooting guide when you book:

(403) 873-7779

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Email us, get a reply in 1 business day

Repair Blockage, Pressure Switch, or Inducer Motor

$199, $379, or $899 to $1399 + GST

Mention this diagnosis from the troubleshooting guide when you book:

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day

Repair Wiring or Control Board

$199 or $899 to $1399 + GST

Mention this diagnosis from the troubleshooting guide when you book:

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day

Repair Pressure Switch or Control Board

$379 or $899 + GST

Mention this diagnosis from the troubleshooting guide when you book:

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day

Repair Flame Sensor, Igniter, or Gas Valve

$199, $379, or $899 + GST

Mention this diagnosis from the troubleshooting guide when you book:

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day

Repair Gas Valve or Control Board

$899 to $1399 + GST

Mention this diagnosis from the troubleshooting guide when you book:

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day

Professional Diagnosis Required

$109.95 regular hours call-out & diagnosis fee

Our technician will identify the problem and tell you how much it will cost to repair. Once you know the problem and the cost, you can decide if you want to proceed.

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day