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  1. #1
    Hello All,
    Hope somebody can shed some light on this problem for me....
    Our furnace has electronic ignition, a damper and a Honeywell Programmable Thermostat. The furnace runs when the stat calls for heat, then shuts down. Here's the mystery. About a minute after the furnace stops, it fires up again and runs for approximately 10 secs, then shuts down again.
    Any idea what could be causing this? I've tried 2 thermostats with no difference. Could the damper be causing this?
    Thanks in advance for any suggestions.
    Cheers,
    Phil

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,167
    Does your thermostat have a common, or does it steal power.
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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Apr 2004
    Posts
    7,680
    How old is it? the older furnaces used an adjustable fan limit control and residual heat could bring the fan back on after shutdown if improperly set or furnace runs hot.

  4. #4
    beenthere:
    Not sure what you mean by common and stealing power.

    docholiday:
    The furnace is an Olsen Minimax that was installed in 1987. (I think...we just moved into this house in Sept.)

  5. #5
    beenthere:
    Not sure what you mean by common and stealing power. There are 3 wires leading to the thermostat, w, r, y.

    docholiday:
    The furnace is an Olsen Minimax that was installed in 1987. (I think...we just moved into this house in Sept.)

  6. #6
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    Power stealing simply implies that the thermostat doesn't have another source of power other than the circuit which is used to call for heating. (or cooling)

    Most programmable t-stats are either battery powered or connection to a common wire directly from the transformer.

    If you feel comfortable doing so, you can disconnect the t-stat (completely-all wires, if not damage may result) and jump R and W for a minute or so. After that, if the furnace still fires, it is not the thermostat. DO NOT JUMP R AND Y, DOING SO WILL TURN ON THE AIR CONDITIONING AND DAMAGE THE COMPORESSOR IN THIS WEATHER. Given that you have a Y connected, I don't know why there is no G for the fan.

    Wait for someone else to confirm this before following the advice in this post


  7. #7
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Sanibel

    I think Doc hi tit on the head. Most older units can have a thermostat ( tem. linit ) that insures that the fan comes on anytime the limit 'sees' heat. My only question would be is the vent motor turning off as soon as the thermostat is satified. it should run for a few seconds after the heat shuts off to remove the residual heat from the heat exchanger. Or the blower should be timed-delayed off to remove the residual heat.

  8. #8
    The damper may be a bimetal one with no wires hooked up to it this damper is suppose to start closing soon after the furnace shuts down, its purpose was to not let conditined air go up the chimney when there was no furnace operation they were a bad idea, if this is the type of damper that you have it could very well be the problem. If your damper has wires attached to it then this is not the problem and it is probably the limit swith on your furnace turning the fan on because of residual heat, or the switch is just worn out.

  9. #9
    Join Date
    Nov 2001
    Posts
    1,874
    As doc was hinting towards,
    You may have a blower coming on due to the heat in the furnace. And not really the furnace itself coming on.

    Have you changed your filter in the last 3 months ?
    If not, then do so.
    What could be happening is,
    Your furnace heats up, the heat tells the blower to come on. This gets the warm air out to your house, then the t-stat tells the furnace to shut off.
    The blower will run to get rid of the heat the furnace produced. the blower will cool a switch to shut the blower off, but heat still remains in the furnce. the switch re-heats and energizes the blower again. Only for a short time.

    Dirty filters will do this, or a switch is getting old and needs replaced.
    If you try to fail, and succeed.
    Which have you done ?



  10. #10
    As far as I can tell, after the burners go out....the damper closes...the blower runs for a few minutes then stops. I watched the sequence closely and waited for the re-start, to see if it is only the blower that starts up, but, of course, it didn't do it while I was downstairs, watching for it.
    The pleated filters (there are 2 filtered cold air return ducts) are not brand new, but only 6 weeks old, so I doubt they are the culprits. This happens with fresh filters.

    Where is the switch that gets cooled (or heated) to control the blower? Can I meter it to see if it is defective?

    Thanks for all the suggestions and advice.
    Cheers,
    Phil

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