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Old 10-01-2022, 07:42 AM   #1
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Surburban 35K btu furnace shuts off

The furnace blower starts and shuts off at 30 seconds. Then, it does not try again even though the thermostat is calling for heat. If I shut off the thermostat and restart it, then the furnace does the same 30 second blower run and shuts off again. The gas water heater and all the stovetop burners are working fine.
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Old 10-01-2022, 08:00 AM   #2
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How is your 12v system?
The furnace needs to get to a certain speed to evacuate the combustion chamber and to move the sail switch to allow ignition.

If the 12v system isn't working correctly, the fan will run slow and not allow the furnace to light.

Suburban has a good troubleshooting guide in the manual.
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Old 10-01-2022, 08:13 AM   #3
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The battery is showing full charge and no other 12V issues are noted. Do you have a link to the manual?
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Old 10-01-2022, 08:17 AM   #4
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The battery is showing full charge and no other 12V issues are noted. Do you have a link to the manual?
Where are you seeing that the battery is showing full charge?
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Old 10-01-2022, 08:31 AM   #5
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Where are you seeing that the battery is showing full charge?
Just on the inside panel. Don't have my meter with me.
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Old 10-01-2022, 08:34 AM   #6
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Wondering about the propane regulator and don't know if the pressure dial on the regulator should be messed with? It is 924N model regulator.
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Old 10-01-2022, 08:52 AM   #7
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Just on the inside panel. Don't have my meter with me.
If you're hooked up to shore power, the inside panel showing 4 lights does not indicate state of charge. It indicates the converter is charging the battery.
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Old 10-01-2022, 09:13 AM   #8
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If you're hooked up to shore power, the inside panel showing 4 lights does not indicate state of charge. It indicates the converter is charging the battery.
I am hooked up. All other devices in the camper are working fine.
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Old 10-01-2022, 09:24 AM   #9
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Disconnect shore power and start furnace. Look at your panel at same time to see if still shows full charge.
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Old 10-01-2022, 09:45 AM   #10
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Disconnect shore power and start furnace. Look at your panel at same time to see if still shows full charge.
Pulled shore power and battery still showed full charge and just slightly dimmed the fully charged light after about 5 minutes of inside lights being on.
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Old 10-01-2022, 10:30 AM   #11
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How can a DIY wannabe person such as me ever get at this inside accessed furnace to check/clean things without disconnecting everything and not knowing anything about the furnace? Seems to be daunting for sure and guess I will have to try to find a technician to come in and check it out. Again, the fan starts and blows loud, but there is no clicking/ignition, and it shuts off after about 30 seconds. A stuck sail switch ?
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Old 10-01-2022, 10:46 AM   #12
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This may help.
Attached Files
File Type: pdf Suburban-Furnace-Master-Service-and-Training-Manual.pdf (3.62 MB, 41 views)
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Old 10-01-2022, 11:41 AM   #13
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I would buy a multimeter to check actual voltage at battery when furnace starts. If battery is low, sail switch might not close initiating igniter and gas valve opening.
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Old 10-01-2022, 12:07 PM   #14
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I would buy a multimeter to check actual voltage at battery when furnace starts. If battery is low, sail switch might not close initiating igniter and gas valve opening.
I'll be checking that soon. I assume that the furnace issue will not affect the A/C units?
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Old 10-01-2022, 12:33 PM   #15
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When the battery voltage is checked, should the shore power be pulled? Also, is there any other indication that the battery may be low? All else seemed to work well when shore power was pulled. Battery is in its 6th year since newly installed.
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Old 10-01-2022, 03:19 PM   #16
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Just a few things

There are a couple of checks the the furnace makes before igniting. The first one is to check that the impellers (firebox AND cabin air) are spinning at speed. That's why others have suggested to check your battery. They may be incorrect since this check happens pretty quickly in the sequence, not 30 seconds as you have stated.

The next thing that happens is that the impellers are allowed to run for 15 seconds to purge any fuel/air from prior attempts.

Then the gas valve opens and the electronics produce spark ignition. If you turn the heat on and promptly get your head down on the floor near the furnace, you will hear a clunk as the gas valve opens and then click-click-click for seven seconds. as the sparks are generated to ignite the fuel/air. If someone else stands outside with nose near the furnace inlet/outlet, they should smell the fuel at this point. When ignition occurs (hear "whoomp"), it is detected and the furnace runs.

If not, it will go through another purge cycle and ignition attempt. After three such attempts, it will give up and go into "lockout." As you have noted, you have to turn the thermostat to "off" and back to "heat" to reset the lockout.

There are several things that can break.
  1. Gas valve might not be opening (no clunk, can't smell gas at the inlet/outlet port)
  2. Electronics not producing spark (no click-click). Sometimes this is electronics, sometimes you just need to reset the spark gap.
  3. Ignition didn't occur (could be spider webs or mud dauber nests in the inlet/outlet ports)
  4. Furnace ignites but ignition not detected (detector or electronics bad)
  5. But the one that seems to happen most often is the propane regulator by the tanks is starting to fail. They only last 8-10 years. The furnace, because it is essentially turbo-charged, is much more sensitive to fuel pressure than the range or water heater. The range has a secondary regulator and the water heater is normally-aspirated.
I'm going to attach the service manual for the furnace. Don't ignore that line near the front that says to check the propane pressure. I wasted hours checking other things before doing that once. (first-time experience). You can build a manometer in an hour with $5 of parts.

Let us know what you find.
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File Type: pdf Suburban Furnace_Service_Manual.pdf (4.92 MB, 40 views)
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Old 10-01-2022, 07:08 PM   #17
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There are a couple of checks the the furnace makes before igniting. The first one is to check that the impellers (firebox AND cabin air) are spinning at speed. That's why others have suggested to check your battery. They may be incorrect since this check happens pretty quickly in the sequence, not 30 seconds as you have stated.

The next thing that happens is that the impellers are allowed to run for 15 seconds to purge any fuel/air from prior attempts.

Then the gas valve opens and the electronics produce spark ignition. If you turn the heat on and promptly get your head down on the floor near the furnace, you will hear a clunk as the gas valve opens and then click-click-click for seven seconds. as the sparks are generated to ignite the fuel/air. If someone else stands outside with nose near the furnace inlet/outlet, they should smell the fuel at this point. When ignition occurs (hear "whoomp"), it is detected and the furnace runs.

If not, it will go through another purge cycle and ignition attempt. After three such attempts, it will give up and go into "lockout." As you have noted, you have to turn the thermostat to "off" and back to "heat" to reset the lockout.

There are several things that can break.
  1. Gas valve might not be opening (no clunk, can't smell gas at the inlet/outlet port)
  2. Electronics not producing spark (no click-click). Sometimes this is electronics, sometimes you just need to reset the spark gap.
  3. Ignition didn't occur (could be spider webs or mud dauber nests in the inlet/outlet ports)
  4. Furnace ignites but ignition not detected (detector or electronics bad)
  5. But the one that seems to happen most often is the propane regulator by the tanks is starting to fail. They only last 8-10 years. The furnace, because it is essentially turbo-charged, is much more sensitive to fuel pressure than the range or water heater. The range has a secondary regulator and the water heater is normally-aspirated.
I'm going to attach the service manual for the furnace. Don't ignore that line near the front that says to check the propane pressure. I wasted hours checking other things before doing that once. (first-time experience). You can build a manometer in an hour with $5 of parts.

Let us know what you find.
Awesome response!
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Old 10-02-2022, 01:21 PM   #18
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Furnace shutting off

I've had the same problem twice. First time it was a sticking sail switch, I temporarily jumpered the sail switch to confirm the problem. Don't run the furnace without a good sail switch. The 2nd time, found a mud dauber (wasp) nest and a stinkbug in the heat exchanger tube, restricting the flow of the combustion gas. Removed both and used an air hose to blow out the heat exchanger to restore normal operation. I had to disconnect the gas line and remove the igniter assembly to get access to the combustion chamber. I also installed insect screens for the furnace, water heater and refrigerator.
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Old 10-02-2022, 03:42 PM   #19
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I love what the DIY'ers know! I fall short of that, but for now I have ordered a new regulator which I can install, and I suppose I can check my battery while the shore power is disconnected and while the camper lights are turned on ?
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Old 10-02-2022, 05:44 PM   #20
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Let us know?

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I love what the DIY'ers know! I fall short of that, but for now I have ordered a new regulator which I can install, and I suppose I can check my battery while the shore power is disconnected and while the camper lights are turned on ?
Keep us posted with your progress.
  • Did you do the sound checks I suggested? The fans blow, right. Did you hear the gas valve open? Did you hear the click-click?
  • Did you look into the furnace intake and exhaust ports on the outside of the trailer, using a flashlight? Did you probe them with a straightened coat hanger? Did you smell the outside exhaust port while running a trial?
  • When you turned the furnace on, how long did it run before the fans stopped? Did you get the three cycles before lockout? The fan would have run continuously, but you would hear three separate gas valve open/closes and click-click cycles.
The regulator is a high-failure rate item, but I don't favor replacing things by guessing--we used to call it Easter-egging. Sometimes it introduces a second problem. Answering some of these questions will rule out other causes.
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