Thermocouple electromagnet - Fiberglass RV

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Old 06-17-2016, 12:20 AM   #1
Junior Member
Name: Emery
Trailer: Boler
Yukon Territory
Posts: 1
Thermocouple electromagnet

I have recently purchased a 1973 boler with a wagonmaster furnace.I am familiar with how a gravity propane furnace works. the furnace has not worked for 10 years or so. The problem is the pilot light not staying lit when releasing the control.
After trying new thermocouples and heating them with a butane torch even, I am most certainly getting the 35mv. that is supposed to be enough voltage to energize the pilot light valve electromagnet that in turn keeps the pilot light valve open, when the push in control is released.
I decided to remove this electromagnet and bench test it. I found that a 1.5vAA battery would most certainly turn it into an electromagnet, but the paltry 35mv was not up the the job. Has anybody out there gone this deep before, and can you provide me with some insight? The windings on the electromagnet do not appear to be damaged or burnt. If there are any retired or current rv furnace mechanics out there, perhaps you have heard of this and it may be a common problem. thanks

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Old 06-17-2016, 03:33 AM   #2
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Name: Raz
Trailer: Trillium 2010
Posts: 3,555
I had a Norcold fridge that wouldn't stay lit. The problem was a design error. There were too many connections and a switch, i.e. too much resistance between the thermocouple and the safety valve. Basically too much voltage drop. Reducing the resistance with larger wire cured the problem.

Perhaps cleaning contacts would help. Did you measure the thermocouple voltage? You can heat the tip with a propane torch, just don't melt the wires . Perhaps the safety valve is corroded and not moving freely. Too much friction, the thermocouple voltage might be too low to move it. WD 40 might help? Let us know what you find. Raz

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Old 06-17-2016, 05:08 AM   #3
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Name: Carl
Trailer: 1981 Trillium 5500
Posts: 314
Although it's probably different from your heater, I also had issues with a Norcold fridge, in which the thermocouple wasn't screwed directly in the control valve but into what they called an "interrupter" which is in fact a switch in series that was allowing the thermocouple voltage to reach the valve only when the switch was on (the switch was activated with the gas/AC/DC mode selector). I don't know the design of your heater, but if it has a similar "interrupter" and it is faulty, you can bypass it to test it. And this interrupter added more contacts points and corrosion possibilities. As mentioned, these valves are very sensitive to voltage drop and all connections from the thermocouple must be very clean.
Also make sure the pilot flame is directed right on the thermocouple. I just corrected an issue on my heater where the pilot burner was clogged and wasn't heating the thermocouple properly and the pilot was going out as I released the start button. Once the pilot burner cleaned, all was good.
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Old 06-18-2016, 07:22 AM   #4
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Name: Joe
Trailer: 1999 Casita 17' SD
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My grandfather repaired hot water tanks with sticking solenoids many many years ago by cleaning and a light coat of white grease.
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