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 Moderated by: RegUS_PatOff, dkpd1581, applianceman18007260692 Search Our Sites for More Info!
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testing a thermocouple  Rate Topic 
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 Posted: Tue Jan 26th, 2010 02:01 am
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handyrandy
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can a thermocouple be tested? and how would I go about it? 

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 Posted: Tue Jan 26th, 2010 03:42 am
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RegUS_PatOff
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dkpd1581 wrote: To actually measure the output of the thermocouple it is easiest to use a digital multimeter set on DC milivolts.  Remove the screwed in portion of your thermocouple (that part that actually goes into the gas valve itself) and hold one meter lead end tightly against the outside part of the thermocouple.  If you have the alligator clips that go to the end of your meter leads it makes this part of the connection easier - if not no biggie.

Looking at the butt end of the side that screws inside of the valve you will see a little section dead center.  It will look like a different colored material surrounded by the outter casing that you have the other end clipped to or held by the alligator clip.  Touch the tip of your other meter lead (the unused free lead)against this material in the dead center/butt end.   Holding the two leads like this while the other end of the thermocouple (tip end that sits in the pilot flame) is in a flame like a candle will cause your meter to read a DC voltage.

A new thermocouple would read up to about 32 milivolts.  As they get older, the voltage will drop and when it gets to about 12-15 milivolts, its time to change them out.

Thats how to measure one for trouble shooting purposes; however, universal thermocouples at Home Depot or Lowes are so cheap and easy to install that its usually easier and less time consuming to just change them out.

Be advised that certain gas valves use what is called a THERMOPLILE which is essentially a gang of thermocouples tied together.  By tying a bunch of thermocouples together you can increase the DC voltage output to 300-500 milivolts.  The reason for this is that with that much DC voltage output, you can run a milivolt thermostat and a milivolt gas valve off of the thermopile.  That gives you all the DC electricity you will need to run your gas water heater off of the pilot light alone - you need no additional source of electricity( no house power, no battery power, nothing).  That is a really cool thing when you want hot water in a location that has no or insufficient electrical resources. 

To know for sure if your gas valve uses a thermocouple or a thermopile, you will need to only look at the name plate of the gas valve and it will tell you.

Hope this helps you a bit.  If your thermocouples are good and the pilot still wants to go out intermittently, look for drafts that may be coming down through the flue or for some other outside source of drafts.  Check and make sure that your pilot is adjusted correctly using the adjustment on the gas valve.  Clean the pilot tube and pilot burner head assembly...best of luck. :dude:



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 Posted: Tue Jan 26th, 2010 04:09 am
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handyrandy
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thank you

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 Posted: Tue Jan 26th, 2010 11:31 pm
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applianceman18007260692
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I have a few magnets I got out of valves with bad operators.
I screw the questionable thermocouple into that and heat it up. I push in spring and if it holds I know the thermocouple is a good un. I do have a millivolt tester in my junk but I use it to test thermophiles and generators.



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