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Thread: Gas furnace seems to "overheat"

  1. #1
    DIY Junior Member
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    Default Gas furnace seems to "overheat"

    I have an induced gas furnace that's about 15yrs old. I'm in Texas. The furnace will run fine for quite a while trying to reach temp but before it gets there it will shut down. It doesn't shut down completely though. The draft inducer motor continues to run and it will restart within a minute (the pilot goes out and relights). When its very cold and running for a long time it will do this several times before reaching the desired temp. When it doesn't need to run very long to get to temp it doesn't happen. It seems to me like the gas flow may be stopping causing the pilot to go out. I tried the following:

    New T-stat
    Clean filter
    Clean furnace/burner area.

    Any idea what this might be?

    Thanks.

    John

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  3. #3
    DIY Junior Member
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    Quote Originally Posted by Doherty Plumbing View Post
    Standing pilot or spark ignition?
    It is electronic spark. There seems to be no hesitation when it restarts. The spark/ignition is immediate.

  4. #4
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by john152 View Post
    It is electronic spark. There seems to be no hesitation when it restarts. The spark/ignition is immediate.
    Figured. Most induced draft appliances are also spark ignition.

    You may want to pull out the flame-rod sensor and clean it up with some emery cloth. If they get coated with products of combustion over time they stop working properly.

    This could be the problem.

  5. #5
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    Quote Originally Posted by Doherty Plumbing View Post
    Figured. Most induced draft appliances are also spark ignition.

    You may want to pull out the flame-rod sensor and clean it up with some emery cloth. If they get coated with products of combustion over time they stop working properly.

    This could be the problem.
    Thanks for the reply. I didn't think that could be my problem since the flame stays on for quite a while before it goes out. I'll give it a try though.

  6. #6
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by john152 View Post
    Thanks for the reply. I didn't think that could be my problem since the flame stays on for quite a while before it goes out. I'll give it a try though.
    Yeah it's unlikely to be it.

    It could be a dusty fan, or a plugged up a/c coil above the furnace if you have one.

    Could also be a high limit that's just starting to fail.

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