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  1. #1
    Join Date
    Apr 2011
    Location
    michigan
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    175
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    Thermopile Failure

    Does anyone use any of the Johnstone brand Thermopiles?? I have been using them, they are lower priced than the Honeywell ones, but it seems every one I have replaced with the Johnstone brand goes bad in about a year. The most recent one was less than a year, still had 600mV pilot signal but would not hold the pilot open. Before replaceing the gas control, I replaced the thermopile and it holds the pilot and energizes the gas control on a call for heat as it should. The pilot was a little high I thought so I lowered the pilot flame and made sure the burners ignited correctly, but even after lowering the pilot flame the thermopile still is constantly cherry red. I have been told they can go bad to over heat, but was wondering if maybe these less expensive ones are junk??? Or if I am missing something. Another unit I had issues with the thermopile would only last about a month, the unit was an empire dv wall furnace and the only thing I was able to determine was the wall thickness was more than what the manufacturer allowed for, the manufacturer said that would cause a shortened thermopile life, on this same unit I also tried the more expensive honeywell brand and it lasted about the same length of time, with this empire dv unit the wall thickness was most likely the issue, but the latest unit is an old boiler.

  2. #2
    Join Date
    Aug 2012
    Location
    NE wisconsin
    Posts
    414
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    I don't see a lot of thermopiles but if I remember correctly the minimum output is 350mV, so if your getting 600 mV maybe the thermopile isn't the problem.

  3. #3
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    7,218
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    Voltage is only part of the equation. A TP can produce 750mv DC but still be bad if it cannot handle the amp draw. A lot of TPs are made in Mexico and failing. You would need to put a load on a TP to see if it is any good just as you would test a car battery.

  4. #4
    Join Date
    Feb 2004
    Posts
    2,832
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    An open read is pretty much useless unless it is low. I've seen thermocouples show an open read of 21-22 or so and show 0-1 under load. Remember the values such as 30mv. 250mv. 750mv are open reads and factory fresh. I always take the clips off the ends if they them. I've seen to many fail and show low reads.

  5. #5
    Join Date
    Feb 2004
    Location
    Ky
    Posts
    284
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    We had 4 or 5 of them from the same parts house go bad. Also seems like the end bulges a little and makes them a pain to remove.
    LN

  6. #6
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    6,780
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    I wonder if White Rogers makes the Johnstone thermopiles? I switched to Honeywell because the are reliable.

  7. #7
    Join Date
    Feb 2004
    Posts
    2,832
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    I think you are correct. They took over the old General Controls co.

  8. #8
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    175
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    Thread Starter
    These thermopiles had bulged ends also when they failed usually end up cutting them to remove them.

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