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  1. #14
    Join Date
    May 2012
    Upper Michigan
    I used to have a pic of me checking millivolts on my phone, I had to delete it because I was in my speedo but anyways the two Leads off the ppile you hook up to them and its vdc, my hs36 just ranges itself to millivolts. If you jump the stat wires at the gas valve and it works you can tell if the valve is bad or good.

  2. #15
    Join Date
    Nov 2009
    Simcoe, ON Canada
    What brand of gas valve is it? I will post a couple of troubleshooting tips tomorrow.
    Does it have a thermocouple and thermopile or just one of the two?
    If you pm me the brand i may be able to give you better suggestions.
    I install and service wall heaters quite often.

  3. #16
    Join Date
    Sep 2003
    One thing to check if the millivolts check out would be a spiderweb in the burner orifice

    The love to get in there and spin a web

  4. #17
    Join Date
    Jul 2006
    clean the pilot and replace the thermopile
    Stuff happens

  5. #18
    Join Date
    Oct 2008
    In a kitchen with my head stuck in an oven
    Make sure your gas supply gas pressure is good (7 to 14"WC - NO MORE than 14" {1/2 psi} though).

    Common issues on millivolt systems:
    1. Weak pilot flame due to improper gas pressure or obstructed pilot burner.
    2. Faulty electrical connections. ANY poor/corroded/oxydized connection can be a major electrical resistance factor at such low voltages.
    3. Faulty operating or limit thermostat.
    4. Weak thermopile. Your pilot stays lit though, so I it may be okay.
    5. Faulty gas valve.

    Typical thermopile output is rated up to 750mVDC, But will drop under load as the main burner is engaged. So, with pilot only, you should read well above 600mVDC. When you set the thermostat to call for heat and main burner coil is energized, thermopile out will drop. You should see a SUSTAINED voltage of around 225 to 250 mVDC (if higher, that's okay) between the "TH" terminals on the combination valve.

    In my experience, the main valve will have problems opening if it's only seeing 175mVDC and less. FYI - pilot lockout usually occurs around 75 mVDC.

  6. #19
    Join Date
    Feb 2004
    PG-9 open read factory fresh-750mv
    G-250 -------------------------250mv
    With the thermostat calling for heat, take reads at the gas valve as follows. 1- Across the PG terminals 2-across the thermostat terminals 3-Subtract 2 from 1 and that is the voltage left to operate the valve. Most systems will operate with 120mv at the valve, however that should be addressed. If you take an open read across the PG and then take a closed read, you will notice a drop in the reads. This is normal and may be as much as fifty percent. If you get a high read across the thermostat terminals, meaning probably 75 or more it is time to check the type of thermostat or poor splices. One of the problems I have encountered with PG's is the clips on the ends. I always remove, brighten wire and connect directly to gas valve terminals. The most COMMON problem: Dirty pilot

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