Gas Furnace – Burner Goes Out

Nov 6, 13 • DIY Tips14 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.

14 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.

  3. will says:

    Hey I have a Colman evcon gas furnace ive checked everything it had a bad high limit it was a 150 I changed it and now the flame and blower shuts off after 3 or 4 min and relights in a few min then blower restarts and repeats should I have a bigger high limit or what I appreciate your help

    • Jim Plummer says:

      Will,

      First, I recommend verifying that high limit you replaced is the component cutting the power to gas valve on your Coleman Evcon gas furnace. This can be done using a multi-meter.

      Second, If the new high limit is cutting the power and it matches the temperature of the old high limit I do not recommend installing a higher temperature. The high limit only cuts out when something else is wrong. Look for something causing reduced air flow through the combustion chamber. A faulty induced draft motor, a restriction in the exhaust pipe or insufficient make up air are places to look.

      A hole in the heat exchanger can also disturb the air flow patterns causing the high limit to cut out. This is an extremely dangerous condition as the gas furnace can leak carbon monoxide gas into the living area of the house and poison the occupants. If you suspect a hole shut down your furnace immediately until you can test it. Call your nearest U-FIX-IT Appliance Parts store if you have any more questions.

  4. Blake says:

    Thanks! Cleaned the fire rod with steel wool and the furnace is working great. Thanks to tips like these, Ive been able to repair all of my HVAC issues for a total of 30 dollars. I can only imagine what a HVAC company would charge!

  5. Gilbert Anguiano says:

    Thank You for the info on this page cause it was very helpful my furnace is now heating

  6. Heather says:

    I have to clean my flame senser about once a month or my furnace stops working. I was told by a friend who does heating and plumbing that I most likely have a crack in my heat exchanger and my whole (14year old) furnace needs to be replaced. We have two co detectors in the basement by the furnace and more on our upper levels which have not detected any problems. Today I noticed that the exhaust pipe that runs from the water heater and connects to the exhaust pipe of the furnace before going up the chimney, is split open along the top side. I taped it closed for now with aluminum tape and my furnace seems to be running fine right now. Could this be my problem?

    • Jim Plummer says:

      Heather,

      Good job spotting the split in the pipe! I always recommend fixing the most obvious problem first. I have been pleasantly surprised how often this practice results in seemingly unrelated problems going away. Yes, this could be what is causing your problem. I recommend replacing the defective exhaust pipe and making certain there are no other leaks in the exhaust pipe.

      Jim

  7. JRigs says:

    Had this problem, dusted my sensors with some brillo and tissue (to remove dust). Fixed! THANKS!

  8. Steve says:

    I live in western Massachusetts and tonight the outside temperature is expected to drop to -14 degrees Fahrenheit (Yes, that’s negative or BELOW ZERO)! My gas furnace was cycling on and off repeatedly and so I turned to Internet searching and came across your site.

    The fix in this post did the trick. I cleaned the sensor with fine sandpaper, put it back together and turned the unit back on. It fired up and has been running fine for over an hour.

    Thanks very much!

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