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  1. #1
    Join Date
    Nov 2008
    Location
    DFW,TX
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    2,170

    standing wall heater, milivolt/microamp volt readings?

    ok so i dont work on a lot of these but on a service call for no heat,

    The pilot lights and stays lit, it puts out voltage to gas valve at around 105Ua, checked the t-stat and it works and i jumped it out just in case and no gas will come out of valve and I also cleaned the the thermocouple and checked all limits.. all seem to be working yet no gas coming from valve.

    So two questions how many micro amps/volts does it take to open the valve and what is the reading supposed to be coming from a flame generated sensor?

    Im pretty sure its the gas valve but just double checking..thanks

  2. #2
    Join Date
    Jul 2010
    Location
    nebraska
    Posts
    1,629
    Good thermocouple should put out around 25 millivolts,no lower than 20. Meter can't be set on microamps to check thermocouples.

  3. #3
    Join Date
    Nov 2009
    Location
    Simcoe, ON Canada
    Posts
    43
    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.

  4. #4
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    460
    are you talking about a thermocouple or a thermopile? above post is good for thermocouple but thermopile is around 750 millivolts. You can tell it is a thermopile as it will be larger than a thermocouple.

    dogboy

  5. #5
    Join Date
    Nov 2008
    Location
    DFW,TX
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    2,170
    Quote Originally Posted by DOGBOY View Post
    are you talking about a thermocouple or a thermopile? above post is good for thermocouple but thermopile is around 750 millivolts. You can tell it is a thermopile as it will be larger than a thermocouple.

    dogboy
    i guess its a thermopile because IT GENERATES THE MILLIVOLTS needed to power the tstat and gas valve on a wall heater.. how do you measure that to make sure its enough.. i had 105 microamps so it was putting out volts so where do i take the reading and whats the normal range?

  6. #6
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    460
    Quote Originally Posted by acguytx View Post
    i guess its a thermopile because IT GENERATES THE MILLIVOLTS needed to power the tstat and gas valve on a wall heater.. how do you measure that to make sure its enough.. i had 105 microamps so it was putting out volts so where do i take the reading and whats the normal range?
    AS stated above generally they put out 750 millivolts. there may be different outputs but the ones I used were 750mv. You got 105 millivolts. So I guess you check it the way you did, with the meter across the thermopile. Microamps has nothing to do with it.

    look at the second page.

    http://www.robertshawtstats.com/spaw...oltSystems.pdf

    dogboy

  7. #7
    Join Date
    Nov 2008
    Location
    DFW,TX
    Posts
    2,170
    Quote Originally Posted by DOGBOY View Post
    AS stated above generally they put out 750 millivolts. there may be different outputs but the ones I used were 750mv. You got 105 millivolts. So I guess you check it the way you did, with the meter across the thermopile. Microamps has nothing to do with it.

    look at the second page.

    http://www.robertshawtstats.com/spaw...oltSystems.pdf

    dogboy
    good link, thanks man..

    BTW im not sure i was using my meter correctly but i was checking with my FP SC 56 meter with the dial select on the uA setting and that where i measure the 105 at across the first two terminals on the block while flame pilot was lit.. what setting on my meter do i use to measure milivolts ?

  8. #8
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    460
    I would say vdc as your meter should auto range down to millivolts. Are you a technician? as this is pretty basic.

    dogboy

  9. #9
    Join Date
    Oct 2011
    Location
    Las Vegas, NV
    Posts
    509
    Quote Originally Posted by acguytx View Post
    good link, thanks man..

    BTW im not sure i was using my meter correctly but i was checking with my FP SC 56 meter with the dial select on the uA setting and that where i measure the 105 at across the first two terminals on the block while flame pilot was lit.. what setting on my meter do i use to measure milivolts ?
    On the sc56, set your meter to volts. Then, press the button to the far left (square with a circle around it) until mV is displayed on the screen. That will read millivolts at that point.

    Sent from my Evo 3D CDMA using Tapatalk 2

  10. #10
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    1,777
    If it is a White Rogers thermopile throw it away and get a Honeywell. I've had so many bad White Rogers t'stats and other parts that I refuse to buy them any more.

  11. #11
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,588
    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.

  12. #12
    Join Date
    Sep 2003
    Posts
    1,675
    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

  13. #13
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,628
    clean the pilot and replace the thermopile
    We really need change now

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