Propane Wall Furnace Pilot Thermocouple?

[yankeerider]

Twenty-plus years ago I installed a Williams brand propane fired wall furnace in my shop. About 4 years ago, I noticed that in the cold weather, the fan would cycle on and off, and it just wasn't putting out the heat that I remembered. I dismantled the burner, and found debris/deposits around the orifices and in the burner tubes. After reassembly, the unit provided great heat, like I remembered from when it was new. However, since I put it back together, there's about a 50/50 chance that the pilot won't stay lit after the main gas valve shuts after the thermostat has been satisfied. I have never had difficulty keeping the pilot lit on a cold start. ( With the price of propane what it is, and this being an occasional use shop, I don't generally leave the pilot going throughout the heating season.)

I suspect that there is a hairline break in the thermocouple tube that sometimes opens when it is hot, thus not proving pilot ignition and shutting down pilot gas. Before I pull this thing apart to replace the thermocouple, has anyone experienced a similar problem that was fixed by thermocouple replacement?

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[grsthegreat]

well, i used to have a pilot lighted water heater years ago....and when the pilot light failed to stay lighted i replaced the thermocoupler (home depot used to stock them... not sure if they do anymore). That fixed the issue.

If the thermocoupler doesnt complete the circuit, the pilot went out.

 

[kenmac]

make sure the pilot flame just contacts the tip of the thermocouple and the connection is snug at the valve connection. Make sure the pilot has a good strong blue flame at the thermocouple tip. You can check thermocouple out put with a vm. With the thermocouple out of circuit you should read about 30 mv with a good strong pilot. You should read .5 or 15 mv with the thermocouple in circuit. You'll have to have an adapter to be able to read mv's in circuit

 

[SPIKER]

I've replaced a few over the years, usually similar issues caused it. On MOST times removal and cleaning of the thermocouple is all that is needed. If the flame don't work at all that is when a replacement was needed.

take it out use some emery cloth sandpaper or similar to "shine up" the end of the thermocouple (end in the pilot flame) AND any connection points to the frame. The voltage is measured between Flame and Ground. A poor ground connection can cause issues as well so make sure the heater Neutral/ground wires are all clean and connected well.

After you have it all clean & reassembled check the Flame (high fire and when switches back to Pilot) to make sure the the MAIN flame is not pulling the pilot flame away from the thermocouple when it shuts down back to pilot.

Mark

 

[tcreeley]

Just order a new Thermocouple. Find your brand and model number off your heater. Go online- type it in and you'll get hits. Find the unit, and manual, get the part number and order on line. Or just get a phone number on line of a retailer and call them and have it sent. The local plumbing supply can order it too for you. They are pretty easy to replace. When they go - not much to do but replace them. I always keep a spare.

-Use it on my tankless lp hot water heater.

 

[yankeerider]

Thanks, all. I've had the new thermocouple for a couple of years now, just working up the initiative to change it out. There's no incentive to do it in the warm weather, and I'm not enthusiastic about working in a 35 degree shop when I need the heat. The thing is, the pilot always lights and stays lit when cold, and the furnace will run for several hours when first started in the cold, so it's only on those days when I want to work out there for most of the day that it's an issue. Thanks for the tip about watching to make sure the main flame doesn't draw the pilot out- i don't think that's it, because I recall having difficulty keeping the pilot lit on a hot relight, but it's fine after 20-30 minutes of cooling.

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