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Old 11-12-2008, 01:05 AM   #1
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outofcontrol's Avatar
1996 28' Excella
Portland , Oregon
Join Date: Jan 2006
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'81 suburban N30M furnace won't re-fire when hot?

I have done many searches, but I think my problem is unique. I've attacked this problem a couple times before and every time I get the research done I go out to work on it and it works perfect. I haven't used the furnace for 4 months and tonight I went out to dive in and fix it and it lit up like a charm on the first try. The problem is when I'm out camping the furnace will cycle a couple times, then at 2 in the morning it doesn't re-light and the fan just blows cold air until the morning or until I turn it off. I've read about low pressure, low voltage, faulty sail switch, limit switch, bad electrode, dirty burner, etc. I really wish it was more of a catastrophic failure that necessitated a replacement, but this old girl keeps tricking me by working so well sometimes. The only time I can get her to fail is when I'm asleep; and not really in the mood for a project.
So in the middle of the night when it fails to light, the fan comes on, I hear the igniter (electrode) clicking but I never hear the flame light. Can I assume that the sail switch and limit switch are working if the board tells the electrode to fire? And if the electrode is activated, can I assume that the valve is getting the same signal? Or will the electrode fire without the valve on? I'm thinking that it's a fuel problem then. Either low pressure, a dirty orifice, or a dirty burner? maybe they're just dirty enough that the residual heat from the last firing makes them inoperable? My pressure test was nothing more than watching all 4 stove burners work at the same time with no signs of slowing, would it change in the night?
I haven't replaced any parts yet in the last endeavors, but it's so hard to pick which one to replace when they all look rusty, dirty, old, nasty...(it's that kind of relationship) And if I replace every part that looked like it needed it, it would be cheaper to buy a new one. If anyone has any ideas before I pull this little girl out again, I'm open for them. Thanks in advance. -Kevin
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1996 Airstream Excella 28'
2007 GMC Duramax 4x4 CCSB
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Old 11-12-2008, 05:48 AM   #2
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1984 29' Sovereign
Savannah , Missouri
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To be quite honest..Replace the darn thing~!
The last thing you want, is to go to sleep at night for the last time~
Trust me when I say this, you'll feel better each morning you wake up..

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Old 11-12-2008, 11:19 AM   #3
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1986 31' Sovereign
Kent , Ohio
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Those old furnaces scare me. I would rather use a quartz heater anyways. why burn my propane when I can use there electricity...

My furnace in my 71 looks new yet.

" Be carefull"
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Old 11-12-2008, 12:02 PM   #4
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1990 25' Excella
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Glenburn , Maine
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Check the continuity of the thermostat wire through a couple of heat/cool down cycles. If that's OK, I suggest you replace the wall thermostat.

Also, how is the condition of your house battery. Is it fully charged and a strong battery or a few years old and questionable? If the latter, it might be the source of your problem IF you have a factory installed LP gas leak detector in the circuit. Mine shuts the system down if battery power is below a threshhold voltage to save the battery...


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Old 11-12-2008, 02:05 PM   #5
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1973 Argosy 26
Norristown , Pennsylvania
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Hi Kevin; Looking at the photo, I seriously cannot see why you bother to repair it. With so much rust it is possible that gas solenoid is sticking. Even when having a very dependable LPG alarm it would scare me to run it. With LPG, it is very seldom that you get a second chance to escape. What if the gas solenoid was leaking for a while and then suddenly lit? Replace it, and that is a sound advice. Thanks, "Boatdoc"
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Old 11-12-2008, 02:55 PM   #6
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1987 29' Sovereign
1971 21' Globetrotter
glen carbon , Illinois
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replace the board. mine did the same thing works fine now
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Old 11-13-2008, 09:31 AM   #7
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1975 Argosy 26
1963 24' Tradewind
Seattle , Washington
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Ok, first, I do think it may be time for a new furnace... that said, my newer NT30 had the same issue.. and then shut off for good on our last trip (fan ran.. but no ignition). I took it in.. new limit switch installed ($83.00). This switch does not allow the furnace to overheat.. which shuts down the furnace. Mine just malfunctioned.. so it was replaced. Heat again!
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Old 11-18-2008, 11:49 AM   #8
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1996 28' Excella
Portland , Oregon
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searching online

I think it's worth looking for a new one. I generally don't like the advice to "just replace it" but on this item, I think the original unit has served it's time. I have a starter in my Tacoma that the shop told me "just replace it" for $375. Turns out I just needed a new set of contacts for $7.50.

I'm going to guess that several of the components on this furnace are near the end of their useful existience, and I would hate to spend $200 fixing it now and have to replace the whole thing next year anyway.

So, does anyone have a good lead on a replacement furnace? I think the one I need is a NT30SP. I just missed one on Ebay for $350, and that seems like the complete bottom deal. Unless I can find someone that ordered the wrong one and has no return option.

BTW, I can't buy an electric heater because I always boondock.

Thanks for all the advice. you guys are a good sounding board. Cheers! -Kevin

1996 Airstream Excella 28'
2007 GMC Duramax 4x4 CCSB
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