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Question DetailsAsked on 2/10/2018

Residue on the thermocouple of my gas fireplace. What can I do?

I have a propane fireplace, the pilot assembly (thermocouple, pilot and thermopile) is brand new and has a nice blue flame.

The problems is that over the period of a couple days, the thermocouple gets covered by some residue and it shuts off the gas valve. The pilot stays on but the main burner shuts off. After a few minutes, the main burner goes back on.
If I clean the thermocouple, the fireplace works fine a couple days until the residue comes back.

The fireplace burns clean, there is no soot on the front glass window.

I would like to know where this residue comes from and what I can do to prevent it.

Thank you!

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Voted Best Answer

Could be an overly hot pilot flame - with propane if there is a hard, intense blue flame with little or no yellow tip, then it could be running hot enough that it is overheating the tip, and the residue is actually surface melted and then oxidizes copper.

Also, if the tip 1/3 or so of the thermocouple is not totally in the blue part of the flame, it could be gas residue (from lower grade gas and also from the odorant, which commonly put a blackish residue on the thermocouple) because the tip is not properly in the blue flame.

The end of the thermocouple is sealed - so any residue on it, unless incredibly thick (like commonly piled-up rust in an older water heater) which actually insulates it from the heat, should have no effect. Sounds to me like it is just marginally in the flame so it is crudding up with soot which then insulates it enough so it kicks out. Check owner's mnual for proper thermocouple placement in the flame.

If this does not help, I guess your choices are to get a different brand new thermocouple (I swear by Honeywell, swear at pretty much any other brand than Robertshaw, which would be my second choice), or call a Heating and A/C or Fireplace specialty contractor to come take a look at it.

Answered 2 years ago by LCD

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