Furnace Kicks Back On

Discussion in 'HVAC Heating & Cooling' started by molo, Jan 20, 2012.

  1. molo

    molo Member

    Messages:
    845
    Location:
    cold new york
    Hello,

    This is a Bryant 80plus. It goes through it's cycle and then kicks back on. But when it kicks back on it doesn't always make it through it's cycle again (in fact the burner doesn't always fire up). This has happened more than a dozen times this week.

    Thanks,
    Bill
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,023
    Location:
    New England
    Not sure what you mean...does it reach the desired thermostat temperature then shut off, or does it short cycle or what?
  3. molo

    molo Member

    Messages:
    845
    Location:
    cold new york
    It will turn off after a full cycle and immediately start to cycle again. This second cycle is often cut short.
  4. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,161
    Location:
    Houston, TX
    Could be the gas pressure. Maybe a frozen regulator if it is outside.

    Among other possibilities.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,023
    Location:
    New England
    The anticipator setting on the thermostat may be wrong for your unit. Also, some thermostats have a differential setting, yours may be set to a smaller number than is good for best operation. If the thermostat isn't in the best location and sees a draft or gets blown on by a register, or sits near the cold air return, or a cold wall next to a room that is unheated, it can do weird things. Also, if it has a dust buildup...take the cover off and check and blow clean. If it's really cold and windy, you might need to think about tightening up the house as drafts in a wall can do things to the sensing on the thermostat. Does the wall feel cold around it?
  6. molo

    molo Member

    Messages:
    845
    Location:
    cold new york
    Thanks for the replies,

    It may be the settings on the thermostat. The thermostat is clean and located on an interior wall. It doesn't show signs of being exposed to cool drafts or isolated temperature variance.

    The furnace will only turn off and kick back on one time per incident. It isn't a short cycling that I've heard before.

    Also, when it kicks back on it will sometimes not even go through the full cycle (sometimes the burners don't even fire up, and you only hear the ignition of the pilot phase). However, at times it will go through the full cycle after it turns off and comes back on again.

    Maybe I should jump the thermostat wires and see how it performs?

    Thanks,
    Bill




  7. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,161
    Location:
    Houston, TX

    You could just set the thermostat about 10 degrees higher than normal and see if it still does that.

    If it is trying to cycle on/off to fast as Jim was saying then it may have a safety system with a built in Delay, Not letting it restart until a certain amount of time has passed.

    If the fan limit switch is turning the fan off to soon, Because the differential is set to close together, That could cause a cycle problem also.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,647
    Location:
    Cave Creek, Arizona
    If the burner does not come on the blower is "harvesting" the latent heat left in the plenum.
  9. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    NEVER "jump" thermostat wires. You can damage the transformer or the control board.\\
  10. molo

    molo Member

    Messages:
    845
    Location:
    cold new york
    Follow Up Info.

    I replaced the thermostat and the problem stopped. I removed the mechanical thermostat (non-mercury) and installed a battery operated non-programmable digital thermostat. The furnace cycles every half an hour instead of every hour, but it does not kick back on.


    Bill
  11. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,161
    Location:
    Houston, TX
    Thanks for the update Bill.

    Sounds like it was a easy fix.

    Nice that you were able to get it working.
  12. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    No doubt. I had a digital thermostat that was bad but still worked. I believe it was causing my low voltage transformer to burn out. I replaced the transformer once and then a few weeks later that transformer went bad. They are easy to change and cheap so I replaced it again thinking it was just defective. A few weeks later it went bad again. So I checked the wiring and all that checked out good so I replaced the thermostat and the transformer and all is good now. That was atleast 3 or 4 months ago.

    While I was at it I replaced my contactor in the outside unit and bought a start and run capacitor just to have on hand. The unit is 12 years old so I expect the capacitors to start going bad soon. I plan on keeping the unit for a few more years.
  13. molo

    molo Member

    Messages:
    845
    Location:
    cold new york
    disregard this post
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