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    itsjeff829's Avatar
    itsjeff829 Posts: 11, Reputation: 1
    New Member
    		  
    #1

    Dec 3, 2008, 03:15 PM
    Testing my gas valve.
    How do I check if the gas valve on my furnace is not working properly. Is there a voltage test I can do on it, and if so, what leads do I put my meter on.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Dec 3, 2008, 04:50 PM
    On most units 24 volts should be supplied to the gas valve when it is supposed to be open.
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
    Plumbing Expert
    		  
    #3

    Dec 3, 2008, 05:25 PM

    How many wires are connected to your gas valve? If only two wires are connected at valve, then you need to put tester leads to these two wires(one lead to one wire and the other lead to the other wire. Should get 24v sometime or another.(when furnace is calling for heat. Need to know things like... is it standing pilot, spark or hot surface ignition, 80 or 90 percent eff. Then we can tell you when you should be getting voltage at gas valve.

    Can you tell us what brand furnace you have. How old is it. The more details you can give, the better we can help.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
    Uber Member
    		  
    #4

    Dec 3, 2008, 06:09 PM

    I think everyone is missing the point here. Pilot, stage 1 and stage 2 are all possible gas valve states.

    If we assume pilot is OK and you have a single stage valve then at least 2 wires should have 24 VAC on them when the gas is supposed to be on. If it does and the gas doesn't turn on, then remove the wires and use the ohms function and test the coil for continuity.

    If the tests above are OK, the valve can still be bad mechanically. There may not be enough gas pressure either.

    Wiring diagrams help a lot.
    MarkwithaK's Avatar
    MarkwithaK Posts: 955, Reputation: 107
    Senior Member
    		  
    #5

    Dec 3, 2008, 06:18 PM

    If you are getting correct voltage to the coil and the valve will not open you can try tapping on the valve housing. Sometimes these things will stick.
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
    Plumbing Expert
    		  
    #6

    Dec 3, 2008, 06:53 PM

    Get the point. If you get 24v at valve while pilot is lit, or spark is sparking, or glow plug is glowing, then bad valve. If no voltage at valve ever, we need to look elsewere for problems.

    Kiss, ohming the valve is a great place to start , not matter what the problem.

    Mark, if indeed 24v at valve, and no gas flow, tapping is also a great recommendation. However if tapping the valve causes gas to flow, time to replace valve.
    MarkwithaK's Avatar
    MarkwithaK Posts: 955, Reputation: 107
    Senior Member
    		  
    #7

    Dec 3, 2008, 07:06 PM

    Yes and no. I have seen them free up and then get stuck all over again and I have seen them free up and run just fine for years.
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
    Plumbing Expert
    		  
    #8

    Dec 3, 2008, 07:21 PM

    I agree. I have seen this also. But I have also learned that when it comes to gas valves, if it failed once, its best to replace, if for no other reason than liability... In theory, a gas valve that sticks shut, could very well stick open.( although I've never found a valve to get stuck fully open, I have found valves that get stuck partially open)
    chate's Avatar
    chate Posts: 1, Reputation: 1
    New Member
    		  
    #9

    Nov 21, 2011, 08:27 PM
    5 wire
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