Heating & Cooling Combined Unit: Why won’t my furnace burners won’t stay lit?

When the furnace burner ignites and only stays on for a few seconds, the flame sensor may be dirty. You can shut off power to the furnace and clean the flame sensor to troubleshoot the problem. You’ll typically find the flame sensor on the front burner box panel but the sensor can be located on the top or bottom of the burner housing as well. Remove the burner access panel and disconnect the flame sensor wire. Remove the flame sensor and clean it with steel wool. Wipe residue off the flame sensor and reinstall it. Reassemble the furnace and test burner operation. If burners stay lit, then cleaning the flame sensor fixed the burner problem. If flames still go out after a few seconds, then you may need to replace the flame sensor.

When the furnace burners only stay lit for a few seconds, a faulty flame sensor may be causing the failure. You can try cleaning the flame sensor to fix the problem. If flames don’t stay lit after cleaning the flame sensor, you’ll likely need to replace it.

Shut off electrical power for the furnace and remove the burner access cover. Disconnect the flame sensor wire and remove the flame sensor mounting screw. Pull the flame sensor out and replace it. Reassemble the furnace and restore electrical power.