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Pilot Lit but burner wont ignite

Post in 'It's a Gas!' started by jwelfeld, Oct 6, 2013.

  1. jwelfeld

    jwelfeld Member

    Joined:
    Jan 28, 2009
    Messages:
    11
    Loc:
    south western CT
    Hi all,

    I have a Vermont Castings SDV30R and I was testing it pre-winter, usually I vacuum the burner/igniter area and I'm all set, but this time the pilot lit is lit but the burner wont ignite. When the switch turns on for the burner (actually connected through a thermostat, new batteries, been working like this for years) nothing happens, but if i press on the pilot starter (piezo?) a few times it will light.

    thanks in advance for any help,

    Joe W.

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  2. blades

    blades Minister of Fire

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    1,576
    Loc:
    WI, Milw
    I do not know the unit, but on a lot of items now the exhaust blower must be running prior to ignition, sensed either by a sail switch or vacuum switch
  3. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    Loc:
    Averill Park, NY, on Burden Lake II...
    Interesting. The piezo has ABSOLUTELY NOTHING to do with the burner, but it could be that you have a loose wire at the terminal block that makes contact when you operate the igniter. Then again, you may have a spider's nest behind the burner orifice that is only partially connected & the additional spark from the piezo may be getting to the gas that leaks past that nest. Make sure everything's tight at the terminal block & maybe pull the burner orifice & clean behind it with a Q-tip. Let us know how you make out...
  4. jwelfeld

    jwelfeld Member

    Joined:
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    Loc:
    south western CT
    I vacuum the area to hopefully remove spider and such will get back to cheching the burner opening again. It seems when I push the piezo the pilot light gets a little bigger and thats what lights the burner
  5. Heatsource

    Heatsource Minister of Fire

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    Loc:
    Northern CA
    check for loose or corroded wires
    debris or rust in the pilot hood- is the flame fully impinging on the thermopile?\
    Mv of t-pile- less than 350, replace
  6. jwelfeld

    jwelfeld Member

    Joined:
    Jan 28, 2009
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    Loc:
    south western CT
    Going to get back to this on the weekend, is there a thread or pot that explains where I make the Mv measurements? does the pilot lite need to no / offf ???? etc....

    thanks in advance
  7. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    Loc:
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    Your stove has a terminal block on the gas valve which has wiring connected to it. The terminals will be marked TP, TH & TH-TP (or TP-TH). The Millivolt reading is generated by the thermopile. That is connected to the terminals with TP (TP = ThermoPile) markings. Simply hold the probes of the multimeter in contact with the screws anchoring the wires to the terminal block. You must have the pilot lit to take the reading.
    HTH
  8. jwelfeld

    jwelfeld Member

    Joined:
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    Messages:
    11
    Loc:
    south western CT
    So I messed around with the connections under the stove and maybe tightened a loose connection and it appears to be working but still looking for more info. I have a thermostat rated as Gas Millivolt thermostat connected to TH and THTP, and then the thermopile looks like its connected to TH and TP. There is a switch on the back of the unit that I removed the connections and wired that to the thermostat (been running like this for years). When I removed the thermostat and put the wires back on the switch it worked every time I threw the switch. When I measure I get 0Mv across the switch and around 250 Mv across TP and TH. When I reconnect the thermostat I get like 60mv across the "Switch" and the same 250Mv across TP and TH. Either way it appears to be working now, but just wondering if anyone can explain how this should work. New batteries in the thermostat.

    Thanks again,

    Joe W
  9. DAKSY

    DAKSY Patriot Guard Rider Staff Member

    Joined:
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    Loc:
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    Your thermostat appears to be hooked up correctly.
    Your thermopile should be connected to the TP & TH-TP labeled terminals. Those same terminals are where you take your milliVolt readings.
    With the switch in the OFF position, your milliVolt reading across the terminals should be 525 +/- 50 mV. When you close the switch (turn the unit ON),
    the milliVolts will drop to 225 +/- 25mV. Your t-stat is a switch, albeit a temperature controlled one. It should be connected to the same terminals as the
    ON/OFF switch on the back of the unit.
    Last edited: Oct 28, 2013
  10. Prairie Pucker

    Prairie Pucker New Member

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    n. Illinois
    I had a similar experience with an old tankless water heater. The voltage generated by the pilot light is very small. If there is *any* corrosion or oxidation that adds electrical resistance anywhere in the millivolt electrical circuit it can cause problems. It can be very sensitive. It's possible that the vibration produced by your piezo ignitor was enough to create a connection. Certainly loosening and/or re-tightening would do the same. The oven burner on the stove has also suffered from the same problem.

    PP

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