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  1. #1

    thermocouple under load conditions

    I have been reading about the thermocouple and how to troubleshoot them underload conditions and no load conditions. It said to use an adapter hooked to the gas vavle and hook the end of the thermocouple to the adapter when you test under load conditions, I was wondering what is the purpose of the under load conditions test if you can test it with the no-load test and is there any way it can be done without the adapter i know how to test the thermocouple with the no-load test can anyone help me out thank you

  2. #2
    Join Date
    Jan 2010
    Location
    Athens GA
    Posts
    1,234
    I know I am a dinosaur but it takes less time to change the thermocouple than it does to troubleshoot it.
    Use good thermocouples like Penn and Penn husky.Check the milivolt rating,sometimes 1 milivolt can make the differance.

  3. #3
    Join Date
    Apr 2002
    Posts
    1,383
    You really need the adapter to test the system properly.

    Without the adapter, you'll typically get 20+ millivolts, and that might drop to zero under the load of a magnet.


    Also, with the adapter you can observe the millivolts at which the magnet drops out. If the magnet drops out at 10 millivolts, you have a bad bad valve. If it drops out at 3 millivolts the magnet is good.

    If everything is working properly, you may get 15 millivolts under the load of the magnet. Blow out the pilot light and observe when the magnet fails ---- if it fails around 3 millivolts then everything is working fine.

    By contrast, if the highest millivolts you get with the pilot lit is 5, then you need to check the pilot flame. If the flame is bad, replace the thermocouple.


    Just changing out the thermocouple is sloppy workmanship. You aren't going to know if the thermocouple is bad, if the magnet is bad or whether you need to check the pilot burner for good operation.

    From time to time you'll find that changing the thermocouple doesn't stop pilot outages---- what do you do then?

  4. #4
    Join Date
    Oct 2009
    Location
    Atlanta,Ga.
    Posts
    196
    It is nice that you want to learn that much about thermocouples,But they are not worth investing much time in.As you know,they are history.I have adapters and a special thermocouple meter,but never use it.If a thermocouple reads 25-30 milivolts(under no load)with a good pilot flame,than it is usually good.if the gas vave pilot will ten not stay lit,the magnet is weak.If you have an adapter,I am fairly certain(if I remember) that under load should be 15-18 millivolts.Make sure that you don't have a crack in the heat exchanger blowing out the pilot light,or a negative pressure sucking it out.Or a strong draft blowing the pilot light out.

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