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    toro5702's Avatar
    toro5702 Posts: 6, Reputation: 1
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    #1

    Oct 23, 2006, 01:16 PM
    Open limit switch on Concord Gas Furnace
    I have a Concord 80 Plus Gas Furnace. I am starting the furnace for the winter and it gives me a LED code of open limit switch or limit switch circuit. Everything seems to work fine up until the point where the blower needs to turn on. I had the same problem last year but got a tech to fix it. I am not sure what he did. Any response would be truly appreciated
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #2

    Oct 23, 2006, 01:58 PM
    Likely he replaced the limit switch. If you can find the receipt from last year, it may tell, maybe even have a part number. It sounds like something is wrong if it needs a new limit switch again or cleaned. Maybe you need a real tech to adjust the air to gas ratio or something.
    toro5702's Avatar
    toro5702 Posts: 6, Reputation: 1
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    #3

    Oct 23, 2006, 06:19 PM
    Thanks for the response but he did not replace anything. I know that for a fact. From what I remember he told me that it was the gas control switch. Supposedly that is what it was. I wasn't there when he got it running right. He told me this afterwards. Well I know I did the same thing last year as I did this year and it is doing the same thing. I know that the gas control switch is on because the burners light up.

    If the limit switch is dirty, where is it located and can I clean it? This house was built in 2004 so the furnace is not old.
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
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    #4

    Oct 23, 2006, 06:41 PM
    It sounds like a main limit as Labman pointed out. Limits can become fatigued if they open and close to many times. The tech may have just reset it by tapping on it, if so, the part should have been replaced. Be sure after the limit is replaced you have good airflow and check the temperature rise. Supply air temp' minus return air temp' should be aprox 35-55 degrees on an 80% furnace. The temp rise should be on the nomenclature panel inside the furnace burner compartment. Be sure filters are changed often and all your registers are open and unobstructed.
    toro5702's Avatar
    toro5702 Posts: 6, Reputation: 1
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    #5

    Oct 25, 2006, 11:00 AM
    Quote Originally Posted by labman
    Likely he replaced the limit switch. If you can find the receipt from last year, it may tell, maybe even have a part number. It sounds like something is wrong if it needs a new limit switch again or cleaned. Maybe you need a real tech to adjust the air to gas ratio or something.
    What does the switch look like and where would it be located? Thanks again
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #6

    Oct 25, 2006, 01:26 PM
    Limit switches used to be short and squat. I think newer ones may be longer and narrower. They are located on the heat exchanger, the tubes the gas flames heat. Should have 2 wires running to the circuit board.
    efr4's Avatar
    efr4 Posts: 1, Reputation: 1
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    #7

    Nov 1, 2006, 03:21 PM
    Quote Originally Posted by toro5702
    I have a Concord 80 Plus Gas Furnace. I am starting the furnace for the winter and it gives me a LED code of open limit switch or limit switch circuit. Everything seems to work fine up til the point where the blower needs to turn on. I had the same problem last year but got a tech to fix it. I am not sure what he did. Any response would be truly appreciated
    Has anyone answered your question?
    toro5702's Avatar
    toro5702 Posts: 6, Reputation: 1
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    #8

    Nov 2, 2006, 09:16 AM
    Quote Originally Posted by labman
    Limit switches used to be short and squat. I think newer ones may be longer and narrower. They are located on the heat exchanger, the tubes the gas flames heat. Should have 2 wires running to the circuit board.
    I believe I found the limit switch. It's a round thing with 2 violet wires and a small hose. How would you go about testing it to see if it works? I can I just connect the 2 violet wires directly while the heater is running to see if the blower turns on?
    toro5702's Avatar
    toro5702 Posts: 6, Reputation: 1
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    #9

    Nov 2, 2006, 09:16 AM
    Quote Originally Posted by efr4
    Has anyone answered your question?
    No not yet.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #10

    Nov 2, 2006, 10:48 AM
    Hose? Sounds maybe more like a pressure switch to signal the inducer is on. Perhaps look some more.
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
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    #11

    Nov 2, 2006, 03:53 PM
    The main limit is mounted to the center of the back wall above or below the burners (depending if it's an up or downflow model.) It is a board usually about 2" x 1 1/4" with 2 wires going to it. It will have a part number and temperature rating on it.
    toro5702's Avatar
    toro5702 Posts: 6, Reputation: 1
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    #12

    Nov 5, 2006, 01:25 PM
    Quote Originally Posted by NorthernHeat
    The main limit is mounted to the center of the back wall above or below the burners (depending if it's an up or downflow model.) It is a board usually about 2" x 1 1/4" with 2 wires going to it. It will have a part number and temperature rating on it.
    I believe I found it. I have a few questions though. Looking at the schematics it says it's the roll-out switch. Is it the same? If so, more or less how much does this part cost? And where can I buy it?
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #13

    Nov 5, 2006, 01:37 PM
    My guess is $10 or less. If it is a generic switch, a HVAC supply should have it. Otherwise, you may need to see your Concord dealer.
    ks67216's Avatar
    ks67216 Posts: 4, Reputation: 1
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    #14

    Oct 8, 2009, 04:52 PM

    I got the same problem but on one of them the inducer runs and it won't light and it doesn't send voltage to the igniter. On the other one it says something about a pressure switch it gives a code of 2 flashes and nothing runs on this one
    viperman99's Avatar
    viperman99 Posts: 1, Reputation: 1
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    #15

    Dec 19, 2009, 12:48 PM
    Northern Heat, your awesome. Helped me out with my furnace in the cold of the night. Thanks

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