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Gas Furnace Not Staying Lit All The Time

Discussion in 'Do It Yourself (Not Computer-Related)' started by ejscarfo, Jan 12, 2019 at 2:45 AM.

  1. ejscarfo

    ejscarfo Thread Starter

    I’ve been fighting with my forced hot air gas furnace on very cold days this year. When the thermostat (which is new), calls for heat, the unit will ignite as it should, but the flame will go out after 5 seconds. The fan will still stay on, blowing cold air tho. It will happen 5 times until the furnace turns itself off, I was told it goes into safe mode. It will sometimes work correctly if I flip the main burner switch off and then on again. It may be working fine after that for a day and then it’s back to the symptoms I note above if the weather is below 32 degrees out. If the weather is above that, there’s usually no issues. Also, the air filter is new and there seems to be no obstructions in the air flow paths.

    I did some research and see that a dirty flame sensor can cause this. I haven’t cleaned it yet because currently the furnace is working as it should. But the next cold snap, I need to not be worried. What should I be looking at?

    Thanks in advance.
  2. cwwozniak

    cwwozniak Trusted Advisor Spam Fighter

    Nov 28, 2005
    First Name:
    The exact style and exact location of a typical flame sensor will depend on the exact brand and model of your furnace. A typical sensor will be a small rod with one end hit by the main burner flame. It is typically mounted to the burner housing through an insulated bushing with a mounting bracket and screw. A wire from the furnace controller attaches to the other end of the rod with a slip-on connector. There are online videos showing the cleaning steps.
    Drabdr likes this.
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