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    wheeloftime's Avatar
    wheeloftime Posts: 12, Reputation: 2
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    #1

    Oct 22, 2008, 02:44 PM
    Goodman gmnt100-4b furnace won't lite
    I have a 4 year old furnace. Igniter glows but will not ignite.then it shuts down. Then starts to recyle again. I have checked voltage at the gas valve and all limit switches. All read 25 volts except one. I was told by a hvac repairman to jump it to see if it is the problem. Jumping made no difference. Im thinking it is the gas valve but can anyone suggest anything? Think twice buy once
    hoseb2000's Avatar
    hoseb2000 Posts: 9, Reputation: 1
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    #2

    Oct 22, 2008, 05:15 PM
    When do you have 25volts at the gas valve. You should only have it for a short time after the ignighter glows and no flame is detected . Check to see if you have condensate in the furnace trap. You could be losing vacuum and sucking air thus not allowing the switches to close and then open the gas valve:eek:
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
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    #3

    Oct 22, 2008, 05:26 PM

    One pressure switch or two?

    If you have two, the first one allows glow plug to come on, the second allows gas valve to come on. Do you ever get 24v at gas valve(as hose asked). If not then I would recommend jumping the pressure switch(the one with the rubber hose coming from the heat exchanger, not the one with the hose coming from the draft inducer). Make sure to jump the terminals after the draft inducer has stared to run. Please let me know if this helps.
    wheeloftime's Avatar
    wheeloftime Posts: 12, Reputation: 2
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    #4

    Oct 22, 2008, 07:45 PM
    It only has one pressure switch.
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
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    #5

    Oct 23, 2008, 03:45 PM
    Quote Originally Posted by wheeloftime View Post
    i have a 4 year old furnace. igniter glows but will not ignite.then it shuts down. Then starts to recyle again. I have checked voltage at the gas valve and all limit switches. all read 25 volts except one. i was told by a hvac repairman to jump it to see if it is the problem. jumping made no difference. Im thinking it is the gas valve but can anyone suggest anything? think twice buy once
    Which one didn't read 24v? There should be a red light on your control board. What is it doing? (flashing, on steady, flash so many times fast and then so many times slow) This light is a diagnostic led and will help us figure out what is happening with your furnace. I highly doubt that it is the gas valve. There are many things to check before buying a new gas valve. I would really like to help you figure this out. Your furnace must be a 80 percenter, metal vent, not plastic?
    wheeloftime's Avatar
    wheeloftime Posts: 12, Reputation: 2
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    #6

    Oct 23, 2008, 03:53 PM
    I have it fixed thank you. I misread one of the voltage readings on the limit switch that attatches to the squirrel cage (fan) 25 volts on one side, 56 on the other. Jumped it ran fine. Bought a new one and she's running fine so far. Now I need to re run the duct work. Existing doesn't seem to be doing the trick. Any good with that?
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
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    #7

    Oct 23, 2008, 04:06 PM

    Maybe I can help, a little out of my leaque. What is the problem with existing ductwork.
    wheeloftime's Avatar
    wheeloftime Posts: 12, Reputation: 2
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    #8

    Oct 23, 2008, 04:42 PM
    Low air flow coming out of certain vents.

    No return air except for the basement. Here's a rough picture of the setup. The house was built in approx 1914.
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
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    #9

    Oct 23, 2008, 06:09 PM

    Should have a return upstairs(main floor) Are you saying that you have good airflow out of some registers? Do you have adjustable supply registers?. I would start by closing down the registers that have good air flow, just a little bit.. Try to balance the system by adjusting your grills.
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