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    SteveF's Avatar
    SteveF Posts: 2, Reputation: 1
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    #1

    Nov 17, 2005, 04:51 AM
    My furnace runs all day
    The burners fire for a minute or two at most then turn off for a minute or two. This repeats all day and it won't get above 64f in the house.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #2

    Nov 17, 2005, 07:07 AM
    Sounds like the lower limit switch is failing to start the blower. Then the furnace get hot enough that the upper limit switch shuts the gas off. As soon as the furnace cools off enough, another cycle starts, on and on. The limit switch supplies 24 volts to a relay, which in turn turns on the blower. If your thermostat has a ''fan on'' position, you can select it, and the furnace should run and warm up the house. Then you can try to track down whether it is the limit switch or the relay. Most relays are now on a control board, hard to trouble shoot and replace. You may have to spend $$$ on a whole new board.
    SteveF's Avatar
    SteveF Posts: 2, Reputation: 1
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    #3

    Nov 17, 2005, 06:45 PM
    Ok, I forgot to mention that the blower runs the whole time.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #4

    Nov 17, 2005, 07:24 PM
    Ok, there is a second limit switch that shuts the gas off if it becomes too hot because the blower didn't start. In this case, it sounds like it is shutting the gas off with the blower on. This is a very important safety feature. I think it is is a normally closed switch, that is current can flow until it gets too hot and then it opens. If you can check it, and without the furnace running, it is not closed, replace it.
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