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Old 2011-12-02, 12:24 AM   #1
TuhuaTarakona
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Default Thermocouple vs Thermopile

What is the difference and how are each used? I see some furnaces that have one OR the other...mine has both and I'm curious as to the difference between the 2?

Thanks!
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Old 2011-12-02, 02:44 AM   #2
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A thermocouple produces just enough power to hold a pilot valve open on a standing pilot appliance.

A thermopile is made up of several thermocouples - capable of producing sufficient power to operate a gas valve. I'm pretty sure that water heaters and gas fireplaces have thermopiles.

The majority of standing pilot furnaces have a thermocouple; residential heating control circuits are normally 24 volts AC. Any furnace which is old enough to have a powerpile should have been scrapped 30+ years ago.
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Old 2011-12-02, 03:41 AM   #3
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Thanks for that txv! I know my Kingsman isn't *that* old - but it still does have a thermopile as well as a thermocouple. Considering that the struggle I'm having is that I can get the pilot light lit, but as soon as I turn on the heat it stays on for 10 minutes and then everything shuts down, gas, pilot light, etc.

So - what I've read is that this is possibly a thermocouple problem? And from your description of the difference of the 2 - and considering that the pilot light gets knocked out, too, it probably is not the thermopile that's bad, but leans towards the thermocouple.

Onward to trying to get it fixed and probably having to just scrap both the couple & the pile and start with new. ...ugh...

Last edited by 57; 2011-12-02 at 10:27 AM. Reason: Unnecessary Quote Removed
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Old 2011-12-02, 04:10 AM   #4
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By furnace, I was referring to a central force air unit with ductwork.

Do you have a wall furnace or boiler?

If the pilot flame is weak, the draft up the flue might be blowing it out at the end of each cycle.

A weak flame can be caused by a dirty orifice; pulling a pilot for cleaning has inherent risks so you might want to call a tech out.

Warning: Never insert a sharp object into a pilot orifice, aside from a broom bristle.
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Old 2011-12-02, 12:22 PM   #5
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I have a freestanding Kingsman naturatl gas heater/stove. It looks just like a wood stove, but uses natural gas.

I was advised to use a stiff wire to clean out the pilot orifice - and considering it appears to be made of very sturdy metal, it might be okay. Yes, I've cleaned out the pilot orifice as well as the burners to the heating unit. The pilot itself, when lit, is a steady blue flame with hints of orange at the tips, so appears to be a good flow of gas and a clean pilot orifice.

The pilot does stay lit for as long as I don't switch it to turn on the heating unit. Once I flip that switch it is either a minute or up to fifteen minutes before it then all shuts down, including the pilot light. ...shrug... The research I've done (and which led me to this forum) says that it might be the thermocouple. So that is my beginning point, but I have to order that from Canada apparently. I have yet to find a US distributor for Kingsman. ?? Maybe someone in this forum knows of one?

I was not sure if I would be wise to replace the thermopile, too, tho. This is where my original question came in as to what the differences were. IF I am going to order the one...I might as well order the other, and may be that would be wise all around even just to have spare parts on hand.

I guess it's Murphy's Law that these types of things only happen once the temperature drops outside and you actually *need* the stove's heat. ...chuckle...
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Old 2011-12-02, 04:41 PM   #6
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Sounds like the thermocouple is fine, given that the pilot stays lit.

It's a strange problem - might want to call someone in who has experience with those units.
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Old 2011-12-02, 10:28 PM   #7
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maybe there is a overheat switch that is malfunctioning. My daughter's fireplace would shut down and it was the overheat switch had loosened and was grounding to the frame.
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Old 2011-12-03, 02:39 AM   #8
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From an absolute amateur. You converted it to NG also. I had an experience with an NG fireplace where the "professional" didn'get venting right and after I read and re-read I pointed out the error. Something could be wrong with venting, conversion, thermopiles, thermocouples, valves, orifices, etc., etc.
It does say in all the docs that only a licenced gas fitter should do what you did and are doing.
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Old 2011-12-03, 11:01 PM   #9
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Quote:
Originally Posted by gzink View Post
From an absolute amateur. You converted it to NG also. I had an experience with an NG fireplace where the "professional" didn'get venting right and after I read and re-read I pointed out the error. Something could be wrong with venting, conversion, thermopiles, thermocouples, valves, orifices, etc., etc.
It does say in all the docs that only a licenced gas fitter should do what you did and are doing.
Is the "you" in your post the OP or me? Nothing is this thread about converting to NG. In another thread I may have mentioned that my daughter's was converted to NG and by a licensed fitter. The switch problem arose and was resolved while it was still on propane
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Old 2011-12-03, 11:54 PM   #10
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The OP states in another thread that he converted it ti natural gas. Post 73 in that thread right after your post in the same thread.
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Old 2012-04-18, 11:39 AM   #11
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A thermocouple generates appox 30 millivolts and normally has a 24 volt operator – A thermopile generates appox 700 millivolts which creates enough voltage so it doesn’t need the extra voltage to operate. So says a rep from RobertShaw who manufactures these things.
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