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Old 12-31-2014, 10:26 AM   #1
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suburban sf 30 backfiring

Does anyone know what causes the furnace to constantly backfire when running. We have the Wildcat hooked up to a large propane tank (100 gallon I think) It seems like when it get to about 30% or lower the furnace starts backfiring. We switched over to the small tanks and it stopped but now it is happening again as the tanks starts to be empty. Do they tend to backfire when the tanks start to get low. I assume it is unsafe to run the heater when it is backfiring. By the way, we have no wasp nests or obstructions and the heater is pretty new so not dirty either.
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Old 12-31-2014, 10:36 AM   #2
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I've not heard of backfiring when the furnace is running. It is a condition that happens sometimes when lighting the furnace if the igniter isn't positioned properly allowing some build-up of propane gas before igniting.


Can you provide more information on the problem?


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Old 12-31-2014, 10:46 AM   #3
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It isn't doing it when the furnace first lights, but after it is running for a while it starts backfiring pretty regularly. Will the tanks going empty perhaps cause low pressure and start the backfiring? That is when it seems to happen.
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Old 12-31-2014, 10:57 AM   #4
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It could point to a problem with your propane regulator. Are you using the same regulator whether running from the 30# and 100# bottles?


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Old 12-31-2014, 10:59 AM   #5
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You could also contact Suburban directly to discuss the problem. Here's their contact info... Airxcel | Suburban Manufacturing Contact Us


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Old 12-31-2014, 11:03 AM   #6
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Did the propane company install a regulator at their tank and then tap into your regulator unknowingly?
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Old 12-31-2014, 11:06 AM   #7
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Thanks for your responses, yes same regulator and we put a new regulator on the last time it was doing the popping/backfiring noise and it seemed to stop but the tanks we also full at the time. I turned the furnace off and back on again and it seems to have stopped for the time being. Maybe as you get to the bottom of the tanks, the propane isn't as good there. I am not sure. I will ask the propane guy when he stops by to refill the tank.
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Old 12-31-2014, 11:11 AM   #8
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I don't think so. I don't see any at the tank. When they installed the tank and the first popping sounds began, we noticed they didn't tighten the valves and it was leaking a little and leaking at the regulator so we stopped the leaks and the popping stopped too but we also changed out the regulator then so not sure which fix solved the problem.
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Old 12-31-2014, 12:38 PM   #9
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When the tanks get low the propane evaporates faster and can cause the propane to freeze which will greatly reduce the pressure. A lot of people will tip the tanks onto their side which works but is considered to be dangerous and I would advise against this practice
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Old 12-31-2014, 12:46 PM   #10
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When the tanks get low the propane evaporates faster and can cause the propane to freeze which will greatly reduce the pressure. A lot of people will tip the tanks onto their side which works but is considered to be dangerous and I would advise against this practice
If that's the case what about a 60 or 100W light bulb to keep the regulator from freezing?

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Old 12-31-2014, 12:49 PM   #11
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Propane will evaporate the same, essentially, regardless of the tank level. and there is no difference full to empty in the propane itself. Something else is going on, such as multiple regulators, a bad regulator, or flow constriction in the piping or line.

I would get your RV to a professional to check out ASAP, not something you want to fool with. A normal propane dealer may be able to troubleshoot this problem as he can check the pressure and flow rate at different points.

Pretty wierd problem.

Could it also be a voltage problem to the 12 side of the circuit, given your battery problems?
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Old 12-31-2014, 02:01 PM   #12
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Sounds like an air and moisture problem. Have a reputable propane dealer purge your tanks.
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Old 12-31-2014, 03:54 PM   #13
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The regulator is not freezing, the propane in the tank freezes and does not evaporate properly. Keep a full tank
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Old 12-31-2014, 04:07 PM   #14
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Quote:
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The regulator is not freezing, the propane in the tank freezes and does not evaporate properly. Keep a full tank
Unless the temp is below negative 45F it will continue to vaporize. It will not freeze, however if there is moisture in the system it will.
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Old 12-31-2014, 04:18 PM   #15
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Unless the temp is below negative 45F it will continue to vaporize. It will not freeze, however if there is moisture in the system it will.
Popping is often caused by insufficient air flow, that is poor supply from fan or restricted by gas passage restriction by nests or combustion gas fouling. Could be simple burner adjustment or worse. Wouldn't operate like that.
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Old 01-01-2015, 12:22 PM   #16
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Thank you for all of your responses. Taking it to a dealer isn't an option right now because my husband was laid off a couple days ago and we are living in it so packing it up and driving to Denver would be a challenge. We filled a small tank and ran it and it didn't pop as long as the tank is full. I will see what happens as it empties. The propane company that fills the big tank wont be around for another week or so. Maybe he can switch out the tank they gave us. That is when the problem seem to start but that could just be a coincidence also.
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Old 01-01-2015, 12:27 PM   #17
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Popping is often caused by insufficient air flow, that is poor supply from fan or restricted by gas passage restriction by nests or combustion gas fouling. Could be simple burner adjustment or worse. Wouldn't operate like that.
We will try to blow the furnace out to see if there is something in it but from just looking thru the intake and exhaust pipes and looking inside the furnace as well as we can see inside, it is very clean. I am not sure what combustion gas fouling means so I will have to google that one.

Thanks
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Old 01-01-2015, 06:46 PM   #18
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Well today we took the shop vac and vacuumed any dust and lint as well as we could and also put it up to the exhaust and intake pipes on the side of the camper and blew thru them. I don't know if that is sufficient to clear the dust and lint etc but the darn thing is beginning to pop again so I am at a loss. I don't think it is the propane tanks because it happens with all of the tanks we fill. Man, this living in an RV is going to drive me insane before it is over. It seems if it isn't one thing, it is the other.
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Old 01-02-2015, 12:01 AM   #19
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The regulator is not freezing, the propane in the tank freezes and does not evaporate properly. Keep a full tank
Propane in a cylinder "freezes" at -44 degrees, at which point it will not longer produce vapor. So that is not likely to be the issue.

Since it happens with multiple tanks that means the likely source is a regulator OR a constriction in the piping itself. As I mentioned, a local propane dealer may be able to pressure and flow test the system without taking it to an RV dealer. I am still guessing that you have a pinched line or guncked up fitting that is restricting the flow to the furnace.

If you could run a separate line from a cylinder directly to the furnace that would check that out, but a better plan would be to have a propane dealer test the line pressure under flow to see how much propane can flow through the line.

Popping in the middle of operation is NOT a good thing.
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Old 01-02-2015, 06:36 AM   #20
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Propane in a cylinder "freezes" at -44 degrees, at which point it will not longer produce vapor. So that is not likely to be the issue.

Since it happens with multiple tanks that means the likely source is a regulator OR a constriction in the piping itself. As I mentioned, a local propane dealer may be able to pressure and flow test the system without taking it to an RV dealer. I am still guessing that you have a pinched line or guncked up fitting that is restricting the flow to the furnace.

If you could run a separate line from a cylinder directly to the furnace that would check that out, but a better plan would be to have a propane dealer test the line pressure under flow to see how much propane can flow through the line.

Popping in the middle of operation is NOT a good thing.
I am going to give them a call today. I think you are right
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