Heater wouldn't work in 1988 Fun Maker w/Suburban furnace so I removed the unit, opened it up, and cleaned out a dirt dobber nest. Now it works, somewhat... when I switch the thermostat on, I get blower, then igniter, flame, and presto, heat! When the temp reaches the thermostat high limit, I get flame-out, then blower continues to run 52 seconds before shut-down. So far, so good.

The next time (after the temp falls below the thermostat low limit,) I get blower, igniter, no flame, and cold air for about 30 seconds before shut-down. This process repeats until I manually switch the thermostat off, then back on, then magically it'll work just fine again for the first cycle, and fail again on the next one.

Any suggestions?

Go to this page and pull up the service manual pdf file. On the eight page it explains the operation of the unit and then goes on to diagnosis. It may help you. It may not be the model of your furnace but may be generic enough to give a general idea of what is happening.

Suburban Furnace Service Manual NT 12S

Check the gas pressure with a gas pressure gauge, I had to replace my propane regulator. My furnace was doing the same thing.

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Les

2006 22ft towlite (replaces 97 21TL)
2006 Toyota tacoma pre-runner 4.0 L V-6 quad cab
w/ 98 chevy Powervision towing mirrors

Thanks for your suggestions and the pointer to the service manual. I had already isolated and excluded gas pressure as the problem. By turning off all lights and disconnecting the fridge, the re-ignition problem seems to occur less frequently and will usually work on one of the retrys before lockout occurs. (Low voltage???) I'm going to pull the burner out again to make sure it is thoroughly clean and free of all the dirt dobber debris, and check the gap on the igniter.

Does anyone know how to get to the sail switch to make sure it is clean and working correctly?

Try cleaning and tightening all the electrical disconnects to and on your furnace, including both slip on connecters and screw downs. Also check the ground connection. Whenever I start having operational issues with older appliances, and other electrical stuff, it seems like half the time just cleaning and tightening up the connections fixes the problem.

On some of the more exposed electrical connections, on our trailer, I apply some dielectric grease to the disconnects to help prevent corrosion and promote conductivity. Just don't use it anywhere near a circuit board!

Jim

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1967 17' Hi-Lo Bon Voyage (1967-1969)
1969 19' Hi-Lo Bon Voyage (1969-2011)
2004 27' Hi-Lo TowLite (2010-present)
2007 Chevy Suburban

Tried just about everything recommended regarding getting the heater started. Just one question: is the blower supposed to come on first , before anything else? We do not hear any clicking sounds, no gas smell, checked the fuses, have 12 volts, have a ground, replaced the thermostat (we had a hi lo years ago and saved all of the parts from it !) Trying to remember all the things we used to do! Just had this 1987 Voyager towed to NJ from NE - great condition, but this furnace will not come on. Did not change the gas regulator yet...any advice is welcome. Chris and Deb

Even something as simple as a spider web in the gas supply tube will hopelessly interfere with proper ignition or burning. I don't know what the answer to this problem is, but I'd love to find one that will keep my patio heater from being invaded by the little critters.

And, I cannot recall for sure if the blower comes on first or not. I think it does, and I know it stays on afterwards to extract the last bit of heat.

- Jack

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Hi-Lo 1707T
2005 F150 4x4 KR SCrew

Yes, on mine the blower comes on first before the burner tries to ignite. When the blower comes on it closes a sail switch to supply power to the ignition control. You will hear the clicking sound then. Mine has a on/off switch on the thermostat that is very hard to move to the on position and a on/off switch on the furnace also. Sounds like you do not have power to the blower. Check for power to the thermostat and thru it to the ignition control. No need to change the regulator or gas valve if the blower is not coming on and you do not hear the igniter clicking. Good luck

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Jim L & Faye
2805C
2003 Silvarado diesel crew cab
central Virginia

This is "off topic" a bit, but I took my thermostat apart and did a little "surgery" on the lever catch. I think I just filed it off a bit. The result is a lever that doesn't feel like you're going to break it when you move it and it doesn't cut into your fingers anymore when you push on it either.

I don't have any pictures, but the "modification" is very obvious once you open the thermostat. (I actually had one at Camping World opened there when I was thinking mine was defective and was going to replace it. I found the new one was just as bad as mine.)

- Jack

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Hi-Lo 1707T
2005 F150 4x4 KR SCrew

Will be working on it again today!