Gas Furnace – Burner Goes Out

Nov 6, 13 • DIY Tips4 Comments

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).

Flame Sensor for Goodman JS L38 035 300x143 Gas Furnace   Burner Goes Out

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.

Flame Sensor for Lennox JS L41 130 300x182 Gas Furnace   Burner Goes Out

The repair

  1. As always, turn off all electrical power to the furnace while you are performing this repair.  Remove the flame sensor.
  2. Steel wool or a fine sand paper can be used to “polish” (clean) the sensor rod and remove the coating.
  3. After cleaning is complete, replace the flame sensor.
  4. 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.

 Gas Furnace   Burner Goes Out

More From Jim Plummer

Jim is an ex-Air Force pilot and a business school graduate of University of Texas at Austin. He has been in the appliance parts business since 1975.

4 Responses to “Gas Furnace – Burner Goes Out”

  1. Kirby Martin says:

    I have a BRyant 80 series heater (HVAC)system. Mine has Puron for the AC.
    I am very interested as to what this problem is cause I am having the same problem. I cleaned the sensor (maybe not good enough?) but the problem
    persists. Cept now the flame will stay on for about 1 or 2 minutes, some
    time maybe up to 5 minutes. but it will flame out quickly. Im considering taking thesensor out and cleaning it again. I now have some 4000 grit sandpaper,
    maybe that will do the job? Will the folling answers be sent to me or do Need to
    come back and check a couple of times daily?
    The guys at my U-Fix-It had realy great guys to deal with. But this is Sunday, I think they close on Sundays…. Kirby

    • Jim Plummer says:

      Yes, cleaning it again is a good idea. It does not take much effort to clean the sensor since the coating is very thin and easy to remove. In addition, you may want to inspect the condition of the ceramic insulator and the wire attached to the sensor for cracks or breaks. Check to make certain the electronic control board has a good ground. The circuit for the sensor is completed through the furnace frame and the ground for the board. Please call back to the store if you continue to have problems. You are right, U-FIX-IT is closed on Sundays to attend church and be with family. Thank you for your inquiry.

  2. keith says:

    I clean flame sensor it still short cycle could it be pressure switch

    • Jim Plummer says:

      In most systems a pressure switch failure will prevent flame ignition. Here are three more items to check. (1)Check for a good connection between the flame sensor and the control. (2)Check the sensor is positioned in the flame. (3)Check the ground for the control board. The pathway for low voltage electricity runs from the control board to the sensor through the flame to the burner back to the control by way of the ground for the control board. If these three steps do not identify the problem, bring the wiring diagram for the furnace to U-FIX-IT and we will help you work out a plan for finding the problem.

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