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Thermocouple

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Joeh1223
Joeh1223 Member Posts: 9
Hello all, my question here is should the thermocouple become bright red when the boilers burners Ignite and turn on?
The thermocouple is a dull red when it’s not on, this might seem like a obvious question I’m not sure tho.

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  • HomerJSmith
    HomerJSmith Member Posts: 2,468
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    Sounds normal.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,335
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    Hi @Joeh1223 , Dull red is good. In my experience, bright red will shorten the life of the thermocouple, even though it's common to see. If you want, there are ways of measuring the output of the thermocouple to see if there is any noticeable difference. FYI, according to an old book, dark blood red is 1050F and full cherry red is 1375F. ;)

    Yours, Larry
  • Joeh1223
    Joeh1223 Member Posts: 9
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    Right @Larry Weingarten But when the burnerns ignite for the heat does the thermocouple stay dull red
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,622
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    Thermocouple temp and color usually doesnt change when the main burners are on or not
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,335
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    Hi, Is the main burner flame hitting the thermocouple? If so, that seems unusual to me. :|

    Yours, Larry
    HomerJSmith
  • Joeh1223
    Joeh1223 Member Posts: 9
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    Weird because mine is definitely heating up when the burners are on, from what I can tell everything looks normal , I will take a video tmrw and post
  • tron_
    tron_ Member Posts: 2
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    As long as it’s receiving the proper voltage to prevent shutoff you’re good to go 
  • Joeh1223
    Joeh1223 Member Posts: 9
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    I just don’t want it to fail because it gets to hot but looking at the boiler the piolt is between two burners don’t really see a way in which it dosent get hot (er)
  • Tim McElwain
    Tim McElwain Member Posts: 4,628
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    Have someone take some millivolt readings when it has been sitting for a while without the burners running. Then take a set of readings after the burners have been on for a while if there is no appreciable change then it is okay. If the open circuit is up a little and the closed circuit increases slightly that is okay. The question then does the system keep operating. If the pilot keeps going out then I would look at possible combustion problem causing the thermocouple to heat up and eventually fail.
  • Joeh1223
    Joeh1223 Member Posts: 9
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    Ok, this is more of a yes or no question LOL
  • mattmia2
    mattmia2 Member Posts: 9,747
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    If the higher temp reduces the life, it spends only a little of its life with the burners on, most of the time it is only heated by the pilot burner. i don't think this is going to appreciably change the life of the thermocouple. some brands may be more durable than others.
  • Gilmorrie
    Gilmorrie Member Posts: 185
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    To prolong life of the thermocouple, shut off the pilot after the heating season - unless you are using your boiler for heating domestic hot water.