Gas Furnace – Burner Goes Out

Nov 6, 13 • DIY Tips32 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

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

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.

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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.

32 Responses to “Gas Furnace – Burner Goes Out”

  1. B Russell Sprout says:

    Hi Jim,
    Let me begin by saying Thank You for your military service! We wouldn’t be an awesome country without selfless veterans like yourself.

    I have a Luxaire gas furnace that is giving me fits! There are 4 burners that are to have a blue flame once the igniter heats the gas. Only 2 of mine light. The one directly behind the igniter and the one beside it. The other two will not light unless I clean the flame sensor which I have done a half dozen times in a week! Used sand paper and emory cloth. I’ve seen flame sensors before that doubled their size due the the build up and they still worked. This one has been shined like a mirror and will only allow one or 2 cycles before the furnace shuts down again! I’m at a loss to explain it! “They” say that sensors rarely go bad and cleaning is about all they need but where am I going wrong! Can you explain?

  2. Shannon says:

    I have a Lennox furnace and my flame sensor is connected to a metal pipe and another piece it does not just come out like I seen in videos. I can take the screw out and clean the top of the sensor but like I said its attached to other pipes and things. Any suggestions would help. My furnace comes on for 1 minute then shuts down. I got a code blinking 7 times and its said its the flame sensor isn’t grounded. I don’t know what that means? Thank you.

  3. John Doe says:

    Nice try, but you’re wrong. The ignition board delivers 90-120V AC low amp through the flame sense rod. The flame rectifies the AC voltage to DC voltage ( the flame is a terrible conductor and only conducts half the sine wave changing the AC to DC voltage) and the ignition board is looking for 3-5 microamps through the ground.

  4. Frank says:

    I too had the same symptoms and after spending over three hundred dollars on a new sensor, control board, and igniter all of which left me with the same problems. The culprit happened to be a Robin decided to build a nest in the chimney stack. Once I cleared it out the heater fired up and worked fine. Since i kept all the parts I replaced I won’t have to spend any money if one of those items should ever go bad.

  5. dan says:

    Had the same problem myself and this fixed it. Thank you, thank you!

  6. John says:

    re-posting, since you deleted and didnt respond to my first inquiry. somehow, I suspect this will be treated the same…

    I have an 8 year old Lennox G43UF-60D-135-06, new home installation. 2800 sqft, 9.5′ ceiling in basement. unfinished. draws from internal room for combustion. Vent pipe from outside for fresh air not blocked. Gas furnace. for 7 years it was fine. Now it is exhibiting the dirty flame sensor – “clean me” every other month. The diagnostic code on the control circuit is always the same – Slow RED flashing LED mated with Fast GREEN Flashing LED (low flame sense detected). It started about a year ago, cleaned flame sensor – was fine for 3 months. Then became worse. (about once a month the error code would return). As of 3/30/15, the flame sensor has been cleaned three and replaced 4 times. Also replaced: Circuit board ($400) and gas control module ($600). 3 different repair businesses have looked at my furnace – yet the problem remains unresolved. About every other month, the flame sensor must be cleaned. (which isn’t an easy task on this model, given its mounting location within the furnace) – flames within the chamber appear normal, blue. air intake has strong suction. no blocked exhaust. filter is replaced on normal intervals. flame sensor isn’t loose and sits well adjusted in the flame. Michigan house. Thoughts, comments – much appreciated. thanks!

    • Jim Plummer says:


      I apologize for the delay. As you are painfully aware, your malfunction is going to be something out of the ordinary. You have been thorough in following all possibilities as they were posited to you. I do not have an easy solution for you. It appears from your narrative that cleaning the sensor corrects the problem when it occurs. This would lead me to look for something that changed in your house at the time your problem began. I would be especially suspicious of anything that changed the composition of the combustion air. Pool chemicals, cleaners, paint, scented candles etc…; anything that might produce fumes that could be sucked into the combustion air. I suspect the problem is external to the furnace and will appear to be totally unrelated. Something changed after 7 years of trouble free operation. The mystery to solve is – what changed? I wish I had something more definite for you. I hope this helps. Please let me know what the problem is when you find it. I would like to know.


  7. Jeremiah says:

    I have a lennox furnace. The furnace burners kick on and run for a couple minutes and then shut down. The ignitor re-lights and the flame kicks on again. Then, the flame shuts down again after about a minute. The ignitor lights up again but, the burners will not re-light. If I shut the thermostat off for about 15 minutes, I can then get the burners to light up again but, the same thing happens where the burners turn off and on. I cleaned the flame sensor but, the same thing happens, again. Thanks.

  8. Susie q says:

    I can tell you the cost…104 to clean and warranty it for a year. The last time I must have had a random acts of kindness vibe going bc the guy cleaned it for free as part of my maintenance contract. I have the same contract but a different serviceman and that is what he charged. But I’m a single woman and afraid of gas, so I’m just happy it’s working now.

  9. 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!

  10. JRigs says:

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

  11. 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:


      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.


  12. Gilbert Anguiano says:

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

  13. 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!

  14. maria graham says:


    My furnace will just stop working. The thermostat if set at 69 and the inside temp is 60 and it shows the unit is heating. The only way to get heat is to turn off unit and restart it. I did replace the thermostat thinking that was bad. Unfortunately it has not stopped the problem.

    I have been reading about this problem and they state I need to clean the flame sensor which has not been cleaned in a while. Do I have to take that out of the
    furnace. Or could this problem be in a board?

    Thanks, Maria

  15. jp says:

    Hi, my suburban sf35 blower runs non stop. Limit switch was replaced after 2 weeks of bypassing (when furnace worked fine while waiting on part). Now the burner seems to fire for about a min but never seems to catch. It is warm in here but the blower constant running is driving me crazy.

  16. Rene Flores says:

    Hi my name rene I am having problems with furnace it keeps short cycling ; I have replaced smartvalue ,control board,high temp limit, and rollout limit any help wuld be much appricated thanks

  17. Cory says:

    I have been having issues with my furnace. The flame lights them goes out right away. I have cleaned the flame sensor several times and it works for a few days and then I have to do it again. Am I not cleaning it good enough? Do I need to buy a new sensor? Could their be another issue? Let me know what you think and thanks for your help.


  18. 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:


      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.

      • Chris M says:

        I have the same flame out problem as described above. Have cleaned the flame sensor, checked all the connections and made sure the ground wire was secure. The problem still persists. The flame stops as soon as the main blower comes on. The system then immediately recycles with the ignition cycle etc. A friend said maybe the controller board is bad and needs to be replaced. Wouldn’t there be other issues if this was the case. What else can i do to diagnose this problem?

        • Emmett says:

          I have the exact same issue. Everything works as it should until blower stars and burners stop immediately. 3 flashes code appears.
          Did you sole this problem? Thank you!

  19. 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.

  20. 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.

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