thermocouple or thermopile

Stan in Oly, WA · Nov 16, 2015

Last month I posted here asking about getting the pilot light to stay lit on a natural gas fireplace. I finally got around to working on it today, and discovered that it has both a thermocouple and a thermopile. Is the thermocouple more likely to be the problem than the thermopile? Should I remove the thermocouple and test it, and if it isn't good, just assume that that's the problem and replace it and leave the thermopile alone? Or are they equally likely to be at fault so that I should remove and test both? Maybe they're very easy to remove so I should just do both at the same time, but maybe not.

Stan

Bob M · Nov 16, 2015

On mine the thermocouple is the flame safety for the pilot. And the thermopile supplies milliamp current to operate the main valve thru the thermostat.

If the t'couple fails the pilot will not stay lit. But if the thermopile is bad the pilot will burn normally but the main valve won't operate.

Both parts are relatively inexpensive. If it were mine I'd replace 'em both.

Mark-Ia · Nov 16, 2015

most likely the Thermocouple is bad.

jeffcat · Nov 16, 2015

I'll go with Bob. At work in the casino guest rooms we have fireplaces in the bigger rooms. All of them have electronic start ignitions with 24 hot surface igniters. Now yours has a thermal couple to hold the safety and a thermal pile for the "t" stat. Thermal couples put out about 125-150 mv. The piles are up in the 500mv range. There are some that go up to 700. The reason I am telling you this is you can measure with you digital meter to see what you have. Change them both cause they are not very expensive and make sure you blow out the little air passage. Those fuzz bunnies make the flame look orange, it should be nice and blue. With LP it will be kinda purple color. Just remember not to over tighten them cause the valves are mostly made of pot metal. Also cross thread really easy.

Dusty MI · Nov 16, 2015

I've never seen where both a thermocouple and a thermopile were used on one heating unit.
If there was not enough power was produced by the thermopile to open the main valve then it was consider safe, even if the pilot was out what little gas came from the pilot would just go up the chimney along with so much air it would not burn/explode.
Power piles were not allow with LP gas, which is heaver than air. Natural is lighter than air.

Dusty

Determined · Nov 17, 2015

A thermocouple is much cheaper and is usually quick and easy to change.
I have replaced dozens of them over the years and they are a fairly common item to fail.

Jerry/MT · Nov 17, 2015

A thermocouple is a single element of two different metals. A thermopile is a group of thermocouples wired together.

thermocouple or thermopile

Stan in Oly, WA

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Bob M

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Mark-Ia

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jeffcat

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Dusty MI

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Determined

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Jerry/MT

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