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Furnace cycles on and off quickly

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  • Furnace cycles on and off quickly

    When my programmable t-stat calls for heat my gas furnace comes on no problem and stays on until the temp. has been satisfied. Then the funny stuff happens.

    When the furnace turns off, after about a minute or so it will come back on for a minute or less, then turn off. Sometimes it will do it a second time.

    It appears that the issue might be with the t-stat because it is, kinda, controlling the furnace and turning it on when calling for heat.

    Any other ideas of what the issue might be?

  • #2
    Re: Furnace cycles on and off quickly

    hello,
    When you say it comes back on do you mean the burner lights up again or is the blower only that is cycling on and off. If its just the blower than the limit might have to be adjusted.

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    • #3
      Re: Furnace cycles on and off quickly

      I will have to check to see if the burner fires or if it is just the blower coming on.

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      • #4
        Re: Furnace cycles on and off quickly

        I had a similar problem with one of my rentals. The pre-exhaust fan would cycle on and off about 30 seconds at a time. Turned out after an hour of testing, I found a short in the line from the thermostat to the furnace. Replaced the wire and it was fine the rest of the winter. One of the staples used to hold the wire to the joist was a little loose, and it wore the covering off of the wire. Very odd.

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        • #5
          Re: Furnace cycles on and off quickly

          Check the amp at the thermostat and see if they match up with the requirement at the control.
          sigpic

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          • #6
            Re: Furnace cycles on and off quickly

            I will look at the t-stat and the control at the furnace. I will also check to verify that it is just the blower cycling an extra time or two after the furnace shuts down and not the burner firing back up.

            I will let you know what I find.

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            • #7
              Re: Furnace cycles on and off quickly

              If it's just the blower than your ductwork is probably a bit undersized.
              sigpic

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              • #8
                Re: Furnace cycles on and off quickly

                duct too small, dirty filter, clogged A/C coil if you have one blocked return or supply vents.

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