How to replace the furnace flame sensor
When furnace burners ignite but only stay lit for a few seconds, a dirty or faulty flame sensor may be causing the problem. Try cleaning the flame sensor and see if the burner flames stay lit. If flames still go out after a few seconds, you may need to replace the flame sensor because it isn't detecting the burner flames.
Disconnect electrical power to the furnace
Turn off the power switch on the side of the furnace or shut off the house circuit breaker for the furnace to disconnect electrical power.
Remove the burner access cover
Remove the access cover in front of the furnace burners.
Remove the flame sensor
Disconnect the flame sensor wire.
Remove the flame sensor mounting screw.
Pull the furnace burner flame sensor out and discard it.
Install the new flame sensor
Insert the new flame sensor and connect the wire.
Reinstall the burner access cover.
Restore electrical power to the furnace
Turn the furnace power switch back on or reset the house circuit breaker for the furnace to restore electrical power.
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