Gas furnace seems to "overheat"

Discussion in 'HVAC Heating & Cooling' started by john152, Dec 25, 2009.

  1. john152

    john152 New Member

    Messages:
    5
    Location:
    Texas
    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
  2. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Standing pilot or spark ignition?
  3. john152

    john152 New Member

    Messages:
    5
    Location:
    Texas
    It is electronic spark. There seems to be no hesitation when it restarts. The spark/ignition is immediate.
  4. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    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. john152

    john152 New Member

    Messages:
    5
    Location:
    Texas
    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. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    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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