Dometic RM24-Burner lights but doesn't stay on. - Fiberglass RV
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Old 06-24-2011, 11:32 AM   #1
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Name: Steven
Trailer: 1975 13' Trillium / 2010 13' Scamp
Ontario
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Dometic RM24-Burner lights but doesn't stay on.

I've got a very nice 1975 Trillium 1300; bought it about 3 years ago. We ran the Dometic fridge on propane for 2 summers and it worked very well. But this year, after lighting the burner, it goes out immediately after releasing the blue plunger. Tried many times at different thermostat settings; sometimes holding the blue plunger depressed for up to a minute. The burner always lights right away and I can see a flickering yellow flame through the view port. But the flame always goes out as soon as the plunger is released.

I've taken precautions to level the trailer; wind doesn't seem to be the problem; ambient temperature is about 23 C.

Any help greatly appreciated.

I'm a licensed mechanic, so if you'd like to suggest some serious dismantling, and can provide the details of the method, I'd be happy to dig in.

Alternatively, if you can recommend a good repair shop in the Toronto area that might be good too.

Thanks very much.
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Old 06-24-2011, 12:01 PM   #2
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Trailer: 2018, 21ft escape— 2019 Ram 1500 Laramie
NW Wisconsin
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It sounds like a thermocouple problem . Thermocouple may be bad,dirty or bad connection at valve body . Second option is that flame is not hitting thermocouple at the right spot or flame is hampered by dirt or insect webs. The pushbutton is usually a manual bypass of the pilot valve so you can get the pilot light lit and then once the pilot flame is sensed the pilot valve is held open electrically by the milivoltage generated by the pilot flame hitting the thermocouple .
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Old 06-24-2011, 12:12 PM   #3
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Trailer: 1975 13' Trillium / 2010 13' Scamp
Ontario
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Steve,
Thanks for your reply; sounds like an excellent diagnosis.
Is there a way to visually confirm the thermocouple is positioned correctly? I've removed a few sheet metal covers, but still not able to directly view the thermocouple.
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Old 06-24-2011, 04:21 PM   #4
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I would check the burner for obstructions like spider webs or wasp nest blocking the combustion air. ( the flame should be blue )
When you have a blue flame there should be a inner and a outer flame, the tip of the inner flame should be just touching the thermocouple.

Bill K


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Originally Posted by Steven Potter View Post
I've got a very nice 1975 Trillium 1300; bought it about 3 years ago. We ran the Dometic fridge on propane for 2 summers and it worked very well. But this year, after lighting the burner, it goes out immediately after releasing the blue plunger. Tried many times at different thermostat settings; sometimes holding the blue plunger depressed for up to a minute. The burner always lights right away and I can see a flickering yellow flame through the view port. But the flame always goes out as soon as the plunger is released.

I've taken precautions to level the trailer; wind doesn't seem to be the problem; ambient temperature is about 23 C.

Any help greatly appreciated.

I'm a licensed mechanic, so if you'd like to suggest some serious dismantling, and can provide the details of the method, I'd be happy to dig in.

Alternatively, if you can recommend a good repair shop in the Toronto area that might be good too.

Thanks very much.
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Old 06-24-2011, 05:03 PM   #5
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Trailer: 2002 19 ft Scamp 19 ft 5th Wheel
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Do what Bill K states and go get some Pipe Cleaners (The kind of pipe you smoke) they are a fuzzy stuff on a wire and run the cleaner through the tube the gas goes through to remove any obstruction. Then look at the PILOT light to make sure it is blue and on the thermocouple. There may B a metal thing on the end of the pilot that directs the flame to the thermocouple.
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Old 06-24-2011, 06:12 PM   #6
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Trailer: 1975 13' Trillium / 2010 13' Scamp
Ontario
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Thanks Bill and Darwin. Will do the pipe cleaner-clean out and post more details tomorrow.
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Old 06-24-2011, 06:45 PM   #7
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Hi: Steven potter... If you need some tech. advice I can recommend our local RV appliance tech www.gammonsrv.com They can even rebuild an older unit to work like new!!!
Alf S. North shore of Lake Erie
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Old 06-24-2011, 08:06 PM   #8
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Name: Tim
Trailer: 2006 Casita
New York
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If you happen to take apart the orifice, don't put anything through it just clean with alcohol . I just took mine apart , and the burner and cleaned them real good. Runs like a top now. Your problem does sound like the Thermocouple , but wouldn't hurt to clean the burner too.
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Old 06-24-2011, 11:25 PM   #9
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I'd start by replacing the thermocouple. They're realatively cheap. Take your old one to any HVAC supplier they'll be able to match it up as they are pretty standard and only a few different sizes and lengths of capilary tubes. 99 % of the time a faulty thermocouple is the cause of your problem.
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Old 06-25-2011, 08:43 AM   #10
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There is a small critter, some kind of a noseeum, that gets in there around the pilot lite and weaves a cocoon. I had this problem for the first time in 1973 and still today.

I was told back then that if I left the pilot on all year, it would prevent that and I did that with that camper. It was a gravity furnace and a real pain to clean out.

With today's water heater I just clean it out at the beginning of the camping season each year because it has easy access.
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Old 06-25-2011, 01:27 PM   #11
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Name: Steven
Trailer: 1975 13' Trillium / 2010 13' Scamp
Ontario
Posts: 7
Problem solved; fridge working fine now. Thank you to everyone who provided suggestions.

I found that the root cause of the problem was a tiny spider web blocking the burner outlet. It was a very small, thin web, but I guess it doesn't take much to block such low pressure.

The blockage at the burner outlet caused the gas to "back up" to the combustion air intake ports, and so when the burning gas exited from that point it burned yellow. Should be something to remember if anyone else is trying to diagnose this kind of problem; proper combustion, as Bill K mentioned is blue.

Trying to see the burner through the small port is very difficult. I found that if you remove the sparker unit (1 screw) from the right side you can use a dental mirror to get a much better look at the burner tube outlet. Mine has a fine wire mesh screen over the end of the tube and the spider must have assumed it was a perfect spot to weave a web!!
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Old 06-25-2011, 03:01 PM   #12
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Trailer: 2006 Casita
New York
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After reading your original post again and I saw where you said it was a yellow flame. I thought the thermocouple just might not be your problem. Glad you got her going, sounds like your on your way to being a Tech (with the mirror and all). Nice when things just work out huh ?
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