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Problem with gas fireplace - Pilot OK but main burner doesn't turn on

Post in 'It's a Gas!' started by SRB, Dec 6, 2012.

  1. SRB New Member

    joined: Dec 6, 2012
    3 posts
    I've got a Mendota DXV-42 gas fireplace that recently stopped working. The pilot lights and remains lit, but the burner will not turn on (i.e. the main valve does not activate).

    I measured the Thermopile voltage with the pilot on at about 700 mV at the wiring terminals, so it doesn't appear to be the Thermopile. I also tried closing (shorting) the thermostat terminals at the wiring block in order to eliminate any possible faults in the thermostat circuit, but the burner will still not turn on.

    Does this imply that the valve itself is faulty, or am I missing something?

    Secondly, if the valve does need to be replaced, can anyone suggest an alternate source for the replacement (Honeywell) valve, or an alternate. The manufacturer will be happy to sell me a new valve, but the cost is $300 - which seems pretty high to me; and will deliver in 2-3 weeks which also seems a little silly.

    Thanks for any suggestions!

    -SRB-
    SRB, Dec 6, 2012
    #1

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  2. DAKSY Super Moderator

    joined: Dec 2, 2008
    3,991 posts
    Averill Park, NY, on Burden Lake II...
    I measured the Thermopile voltage with the pilot on at about 700 mV at the wiring terminals, so it doesn't appear to be the Thermopile.

    That's actually WAY TOO high. Try turning the pilot down to about 550mV.

    When you jumped the terminals did you hear the "click" of the electromagnets in the valve opening to allow the gas to flow to the burner?
    DAKSY, Dec 6, 2012
    #2

  3. SRB New Member

    joined: Dec 6, 2012
    3 posts
    There's no "click" when I jump the terminals. I actually have a 2nd Mendota in another room, and when I jump the terminals on that one it makes a clearly audible "click" when it fires-up - so I know what you're talking about.

    I will adjust the pilot down to see if I can lower the Thermocouple voltage a bit, but I don't hold out too much hope for that to fix the problem.

    (BTW, the voltage on the 2nd Mendota is about 620 mV)

    -SRB-
    SRB, Dec 6, 2012
    #3

  4. DAKSY Super Moderator

    joined: Dec 2, 2008
    3,991 posts
    Averill Park, NY, on Burden Lake II...
    Try "rapping" the valve - in the regulator head area - with the plastic handle of a screwdriver. It's a tad barbaric, but I've seen it work. The second one is too high as well...Turn it down... Running that high will cause premature T-pile failure...
    DAKSY, Dec 6, 2012
    #4

  5. Ironhorse74 Member

    joined: Oct 24, 2009
    176 posts
    The Great Pacific North Wet
    First off Mendota is running a 1200 btu pilot. 700 mv is pretty common on a Mendota. Do not turn down the pilot. Mendota put three different valves on the DXV-42 Robert Shaw, Honeywell and 820 Nova SIT. Does it have a square igniter button on the valve? If so it is a Honeywell. Valve failure on the Honeywell valves is fairly common, The other two not so much.
    Ironhorse74, Dec 8, 2012
    #5

  6. DAKSY Super Moderator

    joined: Dec 2, 2008
    3,991 posts
    Averill Park, NY, on Burden Lake II...
    Really? 1200mV? Don't want to start a war here, but the manual for the DXV-42 cites that the pilot should generate 460mV MINIMUM & the t-pile should read 155mV MIMIMUM with the burner on. Those numbers are in right in line with what I told the OP.
    Please show me more info on these units with the 1200mV system. Seems to me that every millivolt generator (aka Thermopile) that I have ever seen is rated at 750mV MAXIMUM. 1200mV will burn that t-pile out in a few hours. I could be wrong tho, & if you can prove that I am I will admit it.
    DAKSY, Dec 8, 2012
    #6

  7. A1Stoves.com Feeling the Heat

    joined: Dec 19, 2011
    393 posts
    Northern CA
    He is saying BTU(a big flame), not mV
    A1Stoves.com, Dec 8, 2012
    #7

  8. DAKSY Super Moderator

    joined: Dec 2, 2008
    3,991 posts
    Averill Park, NY, on Burden Lake II...
    Doh! Getting dyslexic in my dotage... I'm still thinkin 700 mV sounds high..
    DAKSY, Dec 8, 2012
    #8

  9. SRB New Member

    joined: Dec 6, 2012
    3 posts
    Well. I dismantled the fireplace this morning, checked through all the components and tried about everything I could think of (including giving the valve a few healthy raps) and reassembled... no joy. So I've called and ordered the replacement valve for $300. I'll have to wait a week or two for it to come-in, but at-least should have it functioning when the kids get home form college for Christmas.

    Thanks for all your assistance!

    -SRB-
    SRB, Dec 8, 2012
    #9

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