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  1. #1
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    Nov 2008
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    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
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    nebraska
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    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 2008
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    Bristol Va.
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    569
    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

  4. #4
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    Nov 2008
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    DFW,TX
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    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?

  5. #5
    Join Date
    Nov 2008
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    Bristol Va.
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    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

  6. #6
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    Nov 2008
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    DFW,TX
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    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 ?

  7. #7
    Join Date
    Oct 2011
    Location
    Las Vegas, NV
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    525
    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

  8. #8
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    Nov 2008
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    Bristol Va.
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    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
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    Nov 2008
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    Quote Originally Posted by DOGBOY View Post
    I would say vdc as your meter should auto range down to millivolts. Are you a technician? as this is pretty basic.

    dogboy
    yes and a damn good one but sometimes i run across crap like this that i dont see very often and want to make sure i am doing things correctly.. we are 80% cooling and 20% heating here in DFW,TX and i dont see many Millivolt systems(maybe 6 in 15 yrs) and we typically replace them not repair them so i wanted to brush up on this info..

  10. #10
    Join Date
    Apr 2001
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    MINN
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    Quote Originally Posted by DOGBOY View Post
    I would say vdc as your meter should auto range down to millivolts. Are you a technician? as this is pretty basic.

    dogboy
    Ok its millivolts DC. is the pilot strong? oh well just clean the pilot. in millivolt systems the pilot is the problem.
    then we can go from there

  11. #11
    Join Date
    Nov 2006
    Location
    Athens, Ohio
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    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.

  12. #12
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    Nov 2008
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    Bristol Va.
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    Quote Originally Posted by acguytx View Post
    yes and a damn good one but sometimes i run across crap like this that i dont see very often and want to make sure i am doing things correctly.. we are 80% cooling and 20% heating here in DFW,TX and i dont see many Millivolt systems(maybe 6 in 15 yrs) and we typically replace them not repair them so i wanted to brush up on this info..
    I have not seen one in at least 15 years myself. I think it was in the early 90's. My first hvac job was in dfw for td services.

    dogboy

  13. #13
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    Nov 2008
    Location
    Bristol Va.
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    another double post.

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