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Old 02-18-2007, 11:56 PM   #1
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1979 31' Sovereign
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Suburban Furnace misfires after a while

We tried the furnace on our '79 31ft Sovereign (a Suburban, haven't figured out what model yet). It took a little while for it to start the first time, but now it starts beautifully (it's got an electrostatic ignition system). Turning up the thermostat turns the fan on immediately, and after a few seconds, the furnace lights up. All that is very nice. The flame is mostly blue at the bottom, some yellow at the top.

After about 30 minutes or so, I started hearing "thwoomp" sounds. I took off the cover, and saw that the flame would turn erratic, and, scarily, would leak out through the right side of the metal plate which contains the electrodes and the glass covered viewing hole (a fraction of an inch, but still). The gasket-like material on that plate looks very old and crumbly, so I'm not too surprised that flames _can_ leak out of there, but I don't understand why the flame is irregular.

Naturally, as soon as that happened, I turned off the furnace. I tried a few minutes later, with the same results.

I don't know much about the history of the furnace, but the trailer came with a suburban control board in a cardboard box, which, I'd guess is either the original control board that was replaced, or a replacement control board which was never installed. I _think_ my RV mechanic checked out the furnace when he gave it a once over, but it was july and I wasn't thinking much about furnaces then.

The propane tanks have new regulators and have just been recertified. I've never noticed any variation in LPG pressure on the stove.

What kinds of things could cause the gas mixture to get so out of whack after a while?

I was already planning to 1) get a CO detector, 2) clean out the furnace, since I don't know what state it's in inside. Is there a post somewhere with detailed instructions on how to clean these furnaces? I've heard about forcing air through,but I'm a little puzzled as to the exact steps.

I'd also like to replace the gasket around the electrode-bearing plate. Where should I look for that, and what is it called?

Thanks for any help!

-- David

PS: the airstream is in a remote location (as in, no road or car-ferry!), so "taking it in" is quite a hard and expensive operation. I'd like to fix it myself if possible...
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Old 02-19-2007, 04:08 AM   #2
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Hi David,
obvously, get your tech to have a look at it! This is just a suggestion but I'd guess that you're getting an incomplete combustion - hence the yellowing flame. As a result, the gas is seeking air to complete the combustion - this is available via the gasket leak and its combusting in the gap. The lack of air could be down to a weak fan - although I believe that would be detected by the paddle switch. Perhaps the leak is causing a shortage of pressurised air for combustion and the flame is chasing it? I hope its the gasket $3.49
Marc
ps. go outside and check your inlet/exhaust isn't blocked or obstructed
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Old 02-19-2007, 05:36 AM   #3
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pps. You can get a gasket from Mark'sRV(no relation) at the aforementioned price.

Marksrv.com Suburban RV furnace parts

Marc
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Old 02-19-2007, 10:12 AM   #4
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Here's a picture from the sububan furnace. Any idea what model it is? (so i can replace the gasket?)

Thanks for the pointers. The fan seems quite powerful (and loud =().
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Old 02-19-2007, 10:16 AM   #5
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Gasket closeup

The shape of the gasket doesn't seem to match any of the ones at Mark's RV place. Is this something one cuts up to size?
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Old 02-19-2007, 10:20 AM   #6
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Hang on, I'll look again!
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Old 02-19-2007, 10:21 AM   #7
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Hi Davida,
I'm positive the furnace is an NT of some description. I know the part you mean because I had to replace mine. I dismantled the combustion chamber to check for soot and the gasket disintegrated in my hand. I ordered a new one from MarksRV. If you scroll down the page of the link I sent you earlier it is item No. 0071076(burner access gasket) - it's actually $3.99 - you have to knock out the centre section which actually knocks out again to give you a gasket for the spark electrodes.
Marc
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Old 02-19-2007, 10:36 AM   #8
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Hmm. The shape at the top doesn't look right in the picture, but for 3.99, I'm certainly happy to give it a shot! Thanks!

--david
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Old 02-19-2007, 12:06 PM   #9
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Here is a post from Inland Andy that I saved as a Word doc. It tells you how to clean your heater. This was for a different problem - heater wouldn't re-light after the first heating cycle.
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Old 02-19-2007, 12:21 PM   #10
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Fyrzowt: thanks!
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Old 02-19-2007, 12:56 PM   #11
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Wow, ordering from Mark's RV isn't cheap in canada. Luckily he asked if I really wanted UPS worldwide, which would have been $54!, or Canada Standard at $12.50.
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Old 02-20-2007, 04:38 AM   #12
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Hi Davida,
I didn't think you'd have a problem. I paid $75 to get my gas valve over here - I wanted it fast - in 2 days. I didn't think that USPS et al made any extra charges for delivery to Canada. You could slip this part into your breast pocket and you wouldn't know it was there - you've fallen foul of the minimum charge.
I'm hoping that when you've fitted this the furnace will fire up just fine. This isn't an original part and you'll have to make two little scizzor cuts in it on the tapered upper section to accommodate the holding screws for the electrodes. Be careful doing it. It isn't a compressed card gasket, it's more like a close woven fibre and it can tear.
Yours Aye!
Marc
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