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  1. #1
    Join Date
    Dec 2019
    Posts
    4
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    Furnace shows on but is not?

    Hello all, first time on this forum.
    To start with I have had a professional look at my issue and he cannot seem to resolve the issue.
    It is a weekend property in a rural area so he comes and does his thing says its fine and when I get there Friday night the issue persists. In his defense the issue is strange and not consistent.

    The base issue is the furnace will sometimes drop 5-8 degrees below the set temperature before heat starts coming. That's the basic issue that told us something was wrong.

    I have been watching the thermostat "Honeywell T6" for a few days and this is what is happening.

    The furnace is on and heats up to it's set temp "70F"
    The "heat on" in the top left corner of the thermostat goes off as expected.
    a few minutes later the "heat on" in the top left corner comes back on even though the set temp and room temp are the same.
    The room slowly cools and the thermostat says "heat on" but it is not.
    Eventually the furnace does come on but usually about 5 to 6 degrees below the set temp "70F"

    In laymans terms it's like the furnace thinks its on and heating but its not.

    If I manually drop the temp below the room temp the "heat on" signal goes off
    If I then immediately turn the temp back up the furnace fires immediately.

    Any thoughts, I have no intention of trying to fix this myself but would like to understand and maybe start recommending a course of action to my HVAC guy.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    40,509
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    That's a challenge. Could be stat or furnace. Does your furnace have a window in the door of it that shows a flashing LED? If so that could help diagnose the issue. It will tell if it is getting a call for heat or if it is locked out for some reason.

  3. #3
    Join Date
    Dec 2019
    Posts
    4
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    Thread Starter
    Quote Originally Posted by BaldLoonie View Post
    That's a challenge. Could be stat or furnace. Does your furnace have a window in the door of it that shows a flashing LED? If so that could help diagnose the issue. It will tell if it is getting a call for heat or if it is locked out for some reason.
    Thanks, last time I checked the flashing codes were good. I will check again this Friday when I get there.

  4. #4
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    4,424
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    I would verify there is a signal to W on the furnace even though the stat says it is on.
    UA Local 32 retired as of Jan 2020

  5. #5
    Join Date
    Dec 2019
    Posts
    4
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    Thread Starter
    OK, thank you every one for your help.
    It turns out when I had AC and a new thermostat installed this summer the HVAC tech programmed the furnace as 1 stage and it is a 2 stage. I figured that out myself by going through the thermostat settings.

    I do have some further questions about understanding the 2 stage.
    My other house is a 90 year old double brick with a 20 year old furnace that comes on when it's 2 degrees under the set temp.
    Easy peasy pretty basic.

    The lake place is only 7 years old and hence newer 2 stage furnace and insulated properly.

    It is set to 2 stage a 3 CPH for each stage.
    It seems the furnace just comes on for 10 and off for 10 no matter what the temp is in the room.
    It does seem to keep it at the set temp with very few fluctuations though.
    Is this truly more efficient than just calling heat when you need it?

    Thanks again everyone

  6. #6
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    32,044
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    Have your HVAC technician install a loaner thermostat for you and see if the problem goes away.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

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  7. #7
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
    Posts
    1,605
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    Less cycles per hour is more efficient but may not be as comfortable, more likely to heat past your setpoint and come on below the setpoint. More cycles may short cycle the equipment but keep the temp much closer to what you set it for. Efficiency vs comfort

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