Symptom – Burner lights off, but goes out quickly.
What is it? – This symptom is often caused by a dirty flame sensor that can be easily cleaned. Not all furnaces have a flame sensor, but if your furnace has one, it will be mounted close to the burner with the metal rod positioned in the flame. Flame sensors vary in size (2 to 4 inches) and shape (see examples below). They are powered by a single wire carrying a small amount of electricity (less than 10 DC microamps).
What is happening? – Over time, a coating can form on the metal rod of the flame sensor that is difficult to see. Because of this coating, electricity flow is restricted and the furnace control system “thinks” the burner has failed to light and shuts off the gas as a safety measure even though everything has worked as designed. Flame sensors rarely fail. Broken or cracked ceramic are signs that the flame sensor is defective.
- As always, turn off all electrical power to the furnace while you are performing this repair. Remove the flame sensor.
- Steel wool or a fine sand paper can be used to “polish” (clean) the sensor rod and remove the coating.
- After cleaning is complete, replace the flame sensor.
- Turn the power back on and check the furnace for proper operation.
Note – If this repair does not restore normal operation call for free diagnosis assistance or bring the flame sensor in to the U-FIX-IT Appliance Parts store for free testing and inspection.