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. Book a professional repair or continue to the Flame sensor, Igniter, or Gas valve diagnostic → 

Circuit board failure or control wired incorrectly

Possible faulty wiring or control board. Book a professional repair.

Flame sensed with gas valve off

Possible faulty gas valve or control board. Book a professional repair or continue to the Gas valve diagnostic → 

Gas heating lock out

Continue to the Secondary diagnostic

Gas valve circuit error

Faulty gas valve or control board. Book a professional repair or continue to the Gas valve diagnostic → 

Ignition lock out

Continue to the Secondary diagnostic

Ignition proving error

Continue to the Secondary diagnostic

Igniter fault

Faulty wiring or igniter. Book a professional repair or continue to the Igniter diagnostic → 

Improper main ground or less than 75 volts

Book a professional repair.

Limit or flame roll out switch open

Continue to the Secondary diagnostic

Pressure switch closed when inducer off

Faulty pressure switch or control board. Book a professional repair.

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. Book a professional repair or continue to the Inducer motor or Intake and exhaust diagnostic → 

Secondary voltage fuse

Fuse blown on low voltage circuit. Possible faulty wiring or control board. Book a professional repair.

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Repair Wiring or Igniter

$239 or $419 + 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 Blockage, Pressure Switch, or Inducer Motor

$239, $419, or $999 to $1499 + 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

$239 or $999 to $1499 + 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

$419 or $999 + 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

$239, $419, or $999 + 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

$999 to $1499 + 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

Book a Repair

Starting from $109.95 

Verify the problem, find out the repair cost, then decide if you want to proceed.

Furnace repair price list

Look up the cost of common repairs

(403) 873-7779

Call us 24 hours, 7 days a week

[email protected]

Email us, get a reply in 1 business day