Furnace quit

farmboy84 · 08-28-2019, 07:50 PM

I have a 2009 Laredo with a Suburban NT30SP furnace. We were in Yellowstone two weeks ago and used the furnace every night for 6 nights straight. On the 7th night we ran out of LP in the middle of the night. I switched the tanks over the next day but ever since then the furnace will not light. I turn the heat on from the thermostat, turn the temperature up, the furnace fan will turn on for 15 seconds or so then everything shuts down.

So far I have refilled both tanks to rule out not having LP, and the water heater and stove work fine. The battery is new. I also removed the electrode and cleaned it and tightened the gap since the manual I found online specs 1/8". I am still not seeing any spark through the porthole. I read on another site that a stuck sail switch can cause this issue and a good thud can dislodge it, tried that no luck there either.

The service manual I have been looking at basically comes down to needing a new sail switch or a module board. It's strange that either one of these would go bad coincidentally when I ran out of LP.

Anyone else have ideas? Thanks!

GHen · 08-28-2019, 08:35 PM

Here is an option that’s free.
The regulators are sensitive to quick pressure changes.
Close both tanks, disconnect both tanks.
If you have an auto switchover regulator, switch it to one tank then back to the first one (this step may not necessary, but I do it).
Then connect both tanks again, then SLOWLY open both tanks.
Bleed the air out of the system by lighting the burners on the stove. Then turn the heat on, might take a couple times.

If you still have problems, I’m sure other people will have many other things to check.

farmboy84 · 08-29-2019, 04:52 AM

I did close the tanks and burn off the remaining gas via the stove then opening the tank slowly. I will try again how you suggest, but what gets me is that there is no spark and it shuts down quickly. At the beginning of the year I tested the furnace and I was low on LP and the fan would run for quite a while and it would try to ignite multiple times. Now it doesn't do that.

farmboy84 · 09-06-2019, 02:01 PM

I tried disconnecting the LP and slowly opening it, no change. I took the furnace out of the camper and started to disassemble to look for any apparent issues. I found one prong on the control board that was a nice burnt brown. I have a control board on order with fingers crossed that was the issue.

farmboy84 · 03-19-2020, 03:23 AM

Update to this.

The control board did solve the issue last year and used the camper furnace twice after without issue. I used it this past weekend and it worked fine one night, then the next it quit again with the same symptoms of the fan running but no spark and then shuts down.

The control board physcially looks fine but it's possible it is bad again. I've alsochecked the voltage at the limit switch and is 11v, manual says 12v, close enough? Then I checked the voltage at the sail switch and is 12v until the blower spins fast enough to flip the switch then its 0v, is that correct? Last I checked the voltage at the gas valve and it is 0v. I imagine that needs to be 12v but I don't know if the valve is bad or is the control board or sail switch preventing that?

If the control board went bad again, which the more I think about it, I think is the problem, what could cause the repeated failures? I checked all the wiring in the vicinity and there are no cracked wires or anything that would cause a short.

Summergirl · 03-20-2020, 07:12 PM

Did you replace the board with OEM or Dinosaur board? That might make the difference. Our sail switch was good it was clogged with stuff. Dog hair or insulation not sure but removed it and it was fine.

+Ruff Rider · 03-21-2020, 05:19 AM

I have a 03 and I had this problem. I ran out of gas and when I switched bottles furnace would only light and go out just as fast.

Now I solved this by closing empty tank valve then open new bottle then switch the regulator to the new tank. Heater will fire right up and stay lit.

The furnace will not light and stay working if it senses a almost empty bottle. That way you still have gas for the refer. By closing the old bottle and then switching the tanks keeps air out of the lines. For some reason it this happens the heater refuses to light even if you light the stove.

travelin texans · 03-21-2020, 07:39 AM

Quote:

Originally Posted by +Ruff Rider

I have a 03 and I had this problem. I ran out of gas and when I switched bottles furnace would only light and go out just as fast.

Now I solved this by closing empty tank valve then open new bottle then switch the regulator to the new tank. Heater will fire right up and stay lit.

The furnace will not light and stay working if it senses a almost empty bottle. That way you still have gas for the refer. By closing the old bottle and then switching the tanks keeps air out of the lines. For some reason it this happens the heater refuses to light even if you light the stove.

Or open both bottles & let the auto changeover do it for you as it was designed.
This does require you to check periodically for an empty bottle, but also you won't be outside in the middle of the night swapping tank valves when the open one runs out.

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