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  1. #1
    Join Date
    Sep 2012
    Posts
    373

    SL280v fires off on high stage when fan setting on thermostat is set to "on"

    Our upstairs Lennox furnace always fires off on high stage whenever the fan setting on the thermostat is set to "on" and then switches to low stage 15-20 seconds after. We don't usually keep the blower always on all the time but we decided to try out the fan on mode. The furnace operates normal with the fan set to "auto". Our thermostat is NOT wired for 2 stage.

    Is it normal for the furnace to perform like this with the blower circulating air nonstop? Thanks.

  2. #2
    Join Date
    Dec 2007
    Posts
    4,701
    I would encourage you to watch it in both auto and on. I think you will find it fires in high ALL the time and then drops down.

    Depending on set up, it is either a 2 or 3 stage(if memory serves correct) unit without W2.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  3. #3
    Join Date
    Sep 2012
    Posts
    373
    Thanks for the info. I did monitor both and with the thermostat on auto it ALWAYS fires on low. It's much quieter than when the unit fires on high stage. Just now as I'm typing this the fan is set to "on" and the furnace just fired on high. The SL280v is only 2 stage.

  4. #4
    Join Date
    Dec 2007
    Posts
    4,701
    sorry, got it confused with another unit.

    it is, should be, a 2 stage with timer activating second stage.

    if it truly does as you have said, there is something wrong and you need to call a pro(installing company if new install) and have it fixed.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  5. #5
    Join Date
    Sep 2012
    Posts
    373
    Thanks for the input. I will eventually call a company to come out to look at it. The furnace was installed last July. I did find something in the furnace manual that the installers left right next to the furnace:

    NOTE − If the low fire pressure switch does not close
    the combustion air inducer will switch to high fire. After
    a 15 second pre−purge the high fire pressure switch
    will close and the unit will begin operation on high fire.
    After 10 to 20 seconds of high fire operation the unit
    will switch to low fire.


    I have no idea if this has to do with the problem or not. Hope this helps.

  6. #6
    Join Date
    Dec 2007
    Posts
    4,701
    that could be the issue, but the action ONLY with the fan in on seems coincidental.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

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