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Old 01-29-2006, 10:48 PM   #1
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furnace pilot light problems

Help! My furnace has quit after running beautifully for the last 3 mos. Pilot light won't stay lit. This problem has presented itself 3 times in the last 2 weeks, but was resolved by relighting. Now it won't stay lit.
Can anyone tell me the basic procedure for troubleshooting this proplem?
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Old 01-29-2006, 11:53 PM   #2
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Not sure what type of furnace you have, but you haven't given a lot of info to work with on model or brand that is installed. I am going to guess it's a vintage unit since the new ones are electronic ignition, but I am sure folks that may be able to give some suggestions may need a bit more info to work with......just at thought.....
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Old 01-30-2006, 12:27 AM   #3
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I am cold

sorry...absent minded me!

1975 31' Sovereign, Suburban furnace original to trailer, no model number that I can find.
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Old 01-30-2006, 07:31 AM   #4
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Check the vent tubes

Quote:
Originally Posted by simonhanbury
sorry...absent minded me!

1975 31' Sovereign, Suburban furnace original to trailer, no model number that I can find.
Before you go trying to fix the furnace, make sure it isn't one of the dreaded "recall furnaces". If it is, you will have rubber vent tubes going from the furnace to the outside vent cover. If they are rubber, they will need to be replaced for your health and safety. The hoses crack, and can leak carbon monoxide into the coach. If this happens, you could wake up dead one morning.
Now that I've scared you to death, you may have a bad thermocouple on the furnace. Check the line to the pilot to make sure it isn't blocked, crimped or cracked. Also, check to make sure the pilot sensor (looks like the end of a thermometer) is where the pilot flame will keep it hot, if it has been moved it will think the pilot has gone out, and cut off the gas flow to the furnace.
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Old 01-30-2006, 11:49 AM   #5
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I have not moved the trailer in the last 6 mos. Could a line get cracked all on its own? The problem is that the pilot will not stay lit when I release the gas plunger. I performed a test where I held a lighter to the thermocoupler and lo and behold the pilot stayed lit. I would think this would indicate that the TC is not close enough to the flame to get enough heat. However, how could it move by itself. It has been working perfectly for months and as I mentioned the trailer hasn't moved.

Bad thermocoupler? Should I attempt to push the pilot light closer to the thermocoupler, should I take the coupler out and try to clean it? Does it need a lubricant on the threads where it screws into the holder?

Any ideas? I do not want to start until I have a sound plan of attack.
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Old 01-30-2006, 12:08 PM   #6
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When was the last time you checked the propane level? When you get below 20% in below freezing, the pressure drops dramatically. this can also cause carboning .
I'd start with checking the propane level

good luck
Loren
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Old 01-30-2006, 12:23 PM   #7
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Simon,
I have a 75 Overlander with, I'll bet, a very similar furnace.
When I first got it and tried to get the heat on my pilot also wouldn't stay lit.
What I found was someone had at one time replaced the thermocouple and had destroyed the gasket where the thermocouple and pilot enter the combustion chamber. There is a small plate there that the thermocouple and pilot tube go through that screws to the comb. chamber. That allowed air to enter into the combustion chamber and it would blow out the pilot.
I simply took some hi temp silicone gasket sealer and "caulked" around the plate where the air leak was. Mine is on it's third heating season since I fixed it and it's still working perfectly.
Normally I don't mind taking things apart and fixing them right but i would have had to remove the furnace to do it and that would have meant taking the whole sink cabinet apart to get the furnace out.
Good luck
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Old 01-30-2006, 01:32 PM   #8
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Quote:
Originally Posted by simonhanbury
I have not moved the trailer in the last 6 mos. Could a line get cracked all on its own? The problem is that the pilot will not stay lit when I release the gas plunger. I performed a test where I held a lighter to the thermocoupler and lo and behold the pilot stayed lit. I would think this would indicate that the TC is not close enough to the flame to get enough heat. However, how could it move by itself. It has been working perfectly for months and as I mentioned the trailer hasn't moved.

Bad thermocoupler? Should I attempt to push the pilot light closer to the thermocoupler, should I take the coupler out and try to clean it? Does it need a lubricant on the threads where it screws into the holder?

Any ideas? I do not want to start until I have a sound plan of attack.
The thermocouple may have shifted slightly all on its own, with some help from you when you lit the pilot. Try gently moving it until it's back over the flame of the pilot, and see if it stays lit. I would not try to move the pilot itself, as that can contribute to leaks.
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Old 01-30-2006, 01:32 PM   #9
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Hi all!

Thanks for the suggestions. I have full propane tanks so I do not think it is a low pressure problem. I am located in British Columbia and it hasn't been below freezing for over a month now (spring is here!). I will take a closer look at the thermocoupler today. I think it is the likely culprit as the trailer has not moved and no event can be pointed to that would have affected the set up of the furnace.

Anyone have more suggestions?

OH, I just posted >50 pics of my renovation in case anyone wants to see! look under my member name.
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Old 01-30-2006, 02:56 PM   #10
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good thought

Thanks for the warning regarding moving the pilot light. I had wondered about this. I will attempt to push the TC closer to the pilot flame.
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Old 01-30-2006, 05:53 PM   #11
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Simon,

The thermocouple must be totally engulphed by the pilot flame in order to get it to the proper temp. to hold the gas valve open. It also should be clean, as the burner should be. It sounds like the TC is OK if it will hold the gas valve open when you heat it with another source. Be sure of it's position in the pilot flame. Also, run your stove for 5-10 minutes to purge the gas line just to be sure that there are no air bubbles in it.
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Old 01-30-2006, 05:53 PM   #12
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Pilot trouble

Hello, I had the same trouble a few months ago. If you take the pilot assembly out of the furnace and put it up close to your eye and see if you can see light through it, looking at the sun or a bright flash light. I could not see anything through mine. Get a can of acrysol spray some in it and let it soak for a min and blow it out with an air line. Be sure to blow it backward or opposite the way of gas flow. You will have to do this a few times. After a couple times I could see 3 tiny holes in mine and after a couple more soakings I could see hundreds of very tiny holes and reinstalled it with a new gasket and works like a new furnace. The gasket was all there but it was hard and brittle so I replaced it while it was out. Hopes this helps. Marvin
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Old 02-05-2006, 12:20 PM   #13
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Re: furnace pilot light problems

Quote:
Originally Posted by simonhanbury
Help! My furnace has quit after running beautifully for the last 3 mos. Pilot light won't stay lit. This problem has presented itself 3 times in the last 2 weeks, but was resolved by relighting. Now it won't stay lit.
Can anyone tell me the basic procedure for troubleshooting this proplem?
Simon,

I recently downloaded scans of Suburban Furnace operating instructions from Bryant <http://bryantrv.com/docs2/docs/NT22.pdf>. It has a diagnostic section. Here is the test procedure it describes for the thermocouple and safety pilot valve:

"Therocouples are generally long lived, but failures can occur after a period of use. If the pilot is observed going out during the off cycle, it could be due to either a weak thermocouple or safety pilot valve. A simple check can be made in the field by a time check. Remove the lighter hole cap and extinguish the flame after the pilot has been lit for approximately 5 minutes. Use a watch to check the time that elapses between extinguishing the pilot and the snap of the safety valve. If it is less than 30 seconds, it indicates a weak thermocouple or safety pilot valve. Replace the thermocouple first and repeat the test for the safety pilot valve. If the time lapse is still less than 30 seconds, replace the safety pilot valve."

A whole list of potential air leak points and exhaust restrictions may also be the cause of pilot outage if the problem is something other than the thermocouple and/or safety valve.

I printed out the whole PDF document from bryant. You might want to do the same. It has some very useful info.

Best of luck,
Jeff Stoecker
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Old 02-18-2006, 11:01 PM   #14
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Furnace problems solved!! Thanks for all the help!

I have finally resolved my Suburban NT32Afurnace problems...The problem was that the pilot lights was not full enough to keep the thermocoupler happy. I removed the furnace, removed the pilot assembly and discovered the jets were very blocked. Repeated cleanings and blowing compressed air through it resolved the problem. Gave the whole thing a good cleaning, scrubbed the burners and reinstalled it. The pilot light is bigger than I have ever seen it, and the furnace is working perfectfly. It is no 31 years old and keeping my tin tube warmn and cozy again.

Thanks for all the helpful suggestions. Once again I have learned so much!

Cheers.
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