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    1jimmyd's Avatar
    1jimmyd Posts: 4, Reputation: 1
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    #1

    Mar 8, 2008, 08:46 AM
    Furnace runs then shuts off too early
    My forced air furnace will run for around 5 minutes. Then it will stop but the servo motor will keep running. After another 5 minutes it will fire back up, the fan will kick in and it will start pushing heat. Then it will stop again some times within seconds, sometimes minutes. Does this sound like a High limit switch? If so is there a way to test it? I have put two new thermostats in with no change to the problem.
    Thanks
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Mar 8, 2008, 09:30 AM
    Servo motor

    What is a servo motor?
    1jimmyd's Avatar
    1jimmyd Posts: 4, Reputation: 1
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    #3

    Mar 8, 2008, 09:58 AM
    Hi, I'm not sure of the name of the motor but it's the blower that runs before the main blower and before the burners ignite.
    Thanks
    T-Top's Avatar
    T-Top Posts: 1,871, Reputation: 100
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    #4

    Mar 8, 2008, 06:25 PM
    It's a good chance the main limit is tripping out. Is your return air filter clean and all of your supply grills open? How old is your furnace and what brand is it? The info will help a lot. The small motor is called the inducer motor or vent motor.
    1jimmyd's Avatar
    1jimmyd Posts: 4, Reputation: 1
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    #5

    Mar 8, 2008, 07:31 PM
    Hi the filter is clean and the grill is also. The brand is "4runner" by Goettl. It's about 10 yrs old. If I jumper the hi limit switch it automatically starts the furnace. Is this right?
    Thanks for your help.
    T-Top's Avatar
    T-Top Posts: 1,871, Reputation: 100
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    #6

    Mar 8, 2008, 08:33 PM
    If it works when you jump the high limit you have a air flow problem or bad limit(YOU DO NOT WANT TO BYPASS THE LIMIT AND LET IT GO). I'm not familiar with that system but they all use about the same way of making them work and faulting out.
    1jimmyd's Avatar
    1jimmyd Posts: 4, Reputation: 1
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    #7

    Mar 9, 2008, 06:51 PM
    I'll try to get a limit switch for it and give that a try.
    Thanks for your advice!
    dreed31's Avatar
    dreed31 Posts: 2, Reputation: 1
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    #8

    Jan 4, 2010, 03:24 PM
    Hi mother has an intertherm furnace and it will run fine diring the day but late at night it starts cycling on and off and t stat blinks flinter on and off.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #9

    Jan 4, 2010, 03:57 PM
    Please start a new post for your question.
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