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  1. #1

    Gas fireplace not lighting main burner

    Hi I have a GTI R-3500 natural gas fireplace. ( Heat-N Glo )
    The pilot light stays lit- no problem. When I select the wall switch to ON the main burner does not light.
    I have jumpered the wall switch with no results.Resistance checked in wiring and is good
    I checked the output of the thermopile with the pilot light selected ON and it gives a reading of above 550 millivolts
    The output of the thermopile with the gas valve selected to ON is also in excess of 550 millivolts.
    When I select the wall switch to ON the output from the thermopile drops to only 3 millivolts, which I assume will not open the gas valve being this low. The recommended output from the thermopile with the wall switch ON should be in excess of 100 millivolts.
    Is it normal to have a faulty thermopile give a high reading ( in this case above 550 millivolts ) and when under load ( as in opening the gas valve ) to fall this low.
    Thanks

  2. #2
    Join Date
    May 2005
    Location
    Madison, WI
    Posts
    1,078
    I have seen thermopiles drop to 0 when under load. You could have a failed thermopile or a failed valve. There is a resistance test that can be done to test the valve solenoid.

  3. #3
    Join Date
    Jan 2008
    Location
    Hudson, WI
    Posts
    27
    sounds like you have a wire shorting out. jump the outer 2 terminals of the valve,if unit lights find the wire shorting it out.

  4. #4

    Smile Gas fireplace main burner not lighting

    Problem solved- it was the thermopile.
    Thermopile showed good millivolt reading- in excess of 550mv- when no load applied ( ie. switch not selected to light main burner ) and dropped to 3mv under load (when selecting fireplace ON.)
    Thermopile was the original -10 years old
    Thermopile replaced - fireplace up and running
    Thanks to all for advise.

  5. #5
    Join Date
    Apr 2002
    Posts
    1,383
    Quote Originally Posted by black alder View Post
    Problem solved- it was the thermopile.
    Thermopile showed good millivolt reading- in excess of 550mv- when no load applied ( ie. switch not selected to light main burner ) and dropped to 3mv under load (when selecting fireplace ON.)
    Thermopile was the original -10 years old
    Thermopile replaced - fireplace up and running
    Thanks to all for advise.


    Tricky, isn't it?

    It's especially annoying since the symptoms suggests that the millivolt gas valve is defective, but if you replace the valve the same symtom recurs to remind you that you are a fool.

    The smart test is to get a conventional resistor that is the same as that of the magnet and to measure the milivolts across the resistor. If the millivolts drop to zero across the resistor when doing that test, the thermocouple is bad. If the millivolts stay high, you have a bad gas valve magnet that's shorted out.

    I can't remember the ohms you need ---16 comes to mind but I've been retired too long to remember for sure.

    A mind is a terrible thing to waste.

  6. #6
    Join Date
    Apr 2002
    Posts
    1,383
    Let's see --- that symptom was having the millivolts be good when the wall switch was off, but dropping to zero when the switch was turned on. That looked like the vale operator (not the magnet) was shorting out.

    Doing the test with the resistor allowed you to verify if the thermocouple was the problem.

    I was obviously right about the mind being a terrible thing to waste, anyway.

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