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Old 10-18-2021, 11:06 AM   #1
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No gas to the suburban furnace

Not sure if this is the right spot for this Q.

So my suburban NT-12SE furnace stopped igniting. Worked fine in Spring, No heat in Fall.

The Thermostat triggers the fan no problem. Fan runs fine. There is plenty of propane (and the stove works with good flame so I assume the regulator is functional).
I pulled the electrode and it fires a good spark a few seconds long to ignite a flame but no ignition. I removed and cleaned the burner and reinstalled. I visually inspected the brass burner orifice and it seems clean. I replaced the two gaskets on the combustion chamber burner observation door. The sail switch does its thing (or at least pivots when the fan comes on) not sure what it does but it pivots to the chamber. Small inside unit toggle switch appears to be "on". Still no heat. It seems fairly simple that if the gas is coming into the chamber and the electrode is sending a good spark there should be combustion. So I am 80-90% certain that there is no gas coming into the burner. Something is preventing that. Zero smell of propane inside or outside unit.
I am at a loss for what to check next without pulling the entire unit and getting into gas connections and way in over my head and time availability.

I am wondering from you all if there are any last simple tests I can do to trouble shoot the seeming lack of gas or other aspects that don't require deep disassembly.

much appreciated in advance.
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Old 10-18-2021, 11:33 AM   #2
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Use your volt/Ohm meter to make sure the sail switch is working. Also make sure the gas value solenoid is opening which can be caused by a bad sail switch. There are some great YouTube Videos that can help you trouble shot.
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Old 10-18-2021, 11:34 AM   #3
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Recently went through my NT-12 Suburban furnace. Cleaned it up and tuned it up. They are very simple machines and easy to work on. Yes a bit of a pain, but if you remove it from the van it does give you an opportunity to really go through, clean, and refresh every aspect of the system.

It's possible the gas valve is stuck closed. If this is the case, you might want to replace it for safety reasons.

You can find parts and manuals at the address below. The service manual includes ways to systematically go through the furnace and help find faults. I've attached the applicable service manual for your reference (see page 12).

https://pdxrvwholesale.com/products/...2s-tune-up-kit
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Old 10-18-2021, 12:08 PM   #4
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After sitting all summer it can take numerous attempts to purge the air out of the hose. You can loosen the fitting and crack the valve on the tank to bleed it. Additionally, my regulator got clogged with some kind of waxy, sticky substance that got pumped into the tank somewhere. No gas would flow through it and I had to replace it. Lastly, if you recently had the tank filled and they overfilled it, there is a check valve that prevents liquid propane from flowing. I had to bleed off quite a bit of gas to get it working again.
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Old 10-18-2021, 01:26 PM   #5
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I agree with N147JK. I just went through the heater in our kids van and purchased the tune up kit from pxdrvwholesale. Remove the heater and found a dried up dead bat in the blower. It runs nice now.
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Old 10-18-2021, 01:42 PM   #6
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Quote:
Originally Posted by Bellpilot View Post
I agree with N147JK. I just went through the heater in our kids van and purchased the tune up kit from pxdrvwholesale. Remove the heater and found a dried up dead bat in the blower. It runs nice now.
I found a wasp nest inside the fan housing. Mine was also smelling a little strange a few minutes after it shut down, perhaps like unburnt gas, I'm not sure what it was. But the cleanout cleared it all up - nearly good as new now.

BTW, while it was apart, I also installed some stainless mesh inside the intake and exhaust ports so that the insects can't get in there anymore. Similar to this:
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Old 10-18-2021, 02:07 PM   #7
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Thanks I already have a stainless mesh cap on the outside to prevent any bugs getting in. It looks clear and clean on the inside.
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Old 10-18-2021, 02:12 PM   #8
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Interesting. But wouldn't all this also prevent the propane stove from working?

Earlier this spring I am convinced they overfilled my tank. All summer long it was beyond 85-90% full. Its never worked since but I can't yet tie them to each other as cause and effect. But I have wondered. Its now at 3/4 full and I bled the lines to the stove (via burning the gas until it went out) in case the regulator was tripped somehow. then retried everything. No flame ignition. The fan works fine and so does the electrode spark.
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Old 10-18-2021, 02:21 PM   #9
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It looks clear and clean on the inside.
Only problem is you can't see the inside of the fan housing and steel ducting from the outside - you have take it apart.
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Old 10-18-2021, 02:44 PM   #10
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Quote:
Originally Posted by Clarkboulder View Post
Interesting. But wouldn't all this also prevent the propane stove from working?

Earlier this spring I am convinced they overfilled my tank. All summer long it was beyond 85-90% full. Its never worked since but I can't yet tie them to each other as cause and effect. But I have wondered. Its now at 3/4 full and I bled the lines to the stove (via burning the gas until it went out) in case the regulator was tripped somehow. then retried everything. No flame ignition. The fan works fine and so does the electrode spark.
I found that if you turn the gas off at the tank, then disconnect the gas line at the furnace, you should get a small amount of gas out of the supply line at the furnace. Very little gas escapes, but nonetheless do this in a ventilated area! That should tell you if the furnace line is seeing gas or not.

One simple test you have already done.. smelling for raw gas at the exhaust outlet. If you don't smell any gas after it tries to light several times, most likely the valve is not opening. There are 2 switches inside - the sail switch, which ensures the ventilation system is working, and a limiter switch, which is an over-temperature safety switch. Both have to be working correctly before the gas valve will open.

Finally, with the cover off the furnace, you can check for 12V at the gas valve solenoids (2 of them). If you have 12V, but no gas, the valve is stuck closed. Fortunately, it's easy to replace.
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