suburban sf 30 backfiring

[Witch Doctor]

If you hear a big bang it's delayed ignition. Your valve is letting gas in and when the it fills the chamber the burner will ignite that's a very big bang. What I have read is popping. If your hearing a metal type sound popping that just could be your heat exchanger expanding and contracting. There is a big difference in the sound. If your going to have delayed ignition that would happen every time the burner ignites from when you call for heat. Go outside have some one turn the heat on and you will definitely here it. If it lights off and you don't hear anything and feel heat coming out of the top outlet it is the heat exchanger not the burner. Make sure you have 11" in the water column when the propane man measures it. Propane should be set at 11.5" but for some reason the book say's 11". There is a tap they plug into at the regulator or the gas valve itself to measure it and adjust the pressure.

[Malc]

At the risk of sounding argumentative I will respond again. All the comments are valid but you said you only have the problem when the tanks are low. When propane evaporates it absorbs heat from the liquid propane which cools off the liquid. If the same amount of heat is removed from 30# of liquid as from 100# of liquid the 30# will get a lot colder and will freeze even if the outside temperature is not, as quoted, minus 45 degrees. If the propane bottle is tipped on it's side the surface area of the liquid is increased and will have better evaporation but I do not recommend it.

Sorry about your job situation, been there and I understand the need not to spend money. If your problem disappears when you have a full tank of propane then keep your tanks full but always be careful with propane.

[Witch Doctor]

I just reread some post, Seen you are in Denver, That could be part of the problem with your burner orifice. I would call the service dept at Suburban and ask if you need and require either a different spring in your regulator or a different size orifice for the altitude that you are at. I remember not all that long ago there was a thread that had a warning about camping in higher altitudes.

[garbonz]

A normally operating RV (or other) furnace works FINE in Colorado, although an orifice check may help, they don't routinely do a high altitude change, as far as I have been able to tell. What is disconcerting to me is the OP's quote "constantly backfire when running" which indicated it is not just upon ignition. I have seen and experienced water heaters doing that, but not furnaces.

A reputable propane dealer in Ft. Morgan should be able to troubleshoot your issue and if you have been getting a 100lb tank dropped offf, they may be able to do that at no or reduced charge in return for the business. If they think it needs a new orifice, then they may even be able to do that themselves.

Propane is in routine use out here in the mountain west and frankly a RV furnace does not flow that much propane for it to be a problem for a 100lb tank. SOmething else is probably going on.

[Witch Doctor]

Originally Posted by garbonz

A normally operating RV (or other) furnace works FINE in Colorado, although an orifice check may help, they don't routinely do a high altitude change, as far as I have been able to tell. What is disconcerting to me is the OP's quote "constantly backfire when running" which indicated it is not just upon ignition. I have seen and experienced water heaters doing that, but not furnaces.

A reputable propane dealer in Ft. Morgan should be able to troubleshoot your issue and if you have been getting a 100lb tank dropped offf, they may be able to do that at no or reduced charge in return for the business. If they think it needs a new orifice, then they may even be able to do that themselves.

Propane is in routine use out here in the mountain west and frankly a RV furnace does not flow that much propane for it to be a problem for a 100lb tank. SOmething else is probably going on.

Your right but you need to start some where and I would with the propane company and let them make sure no moisture is in the tanks. here is a little check list for the OP

D. Burner Ignites But Shuts Off:
1. Check to be certain that flame sensor is over slots in the main burner and that the
main burner flame is burning against the tip of the flame sensor - adjust by bending
the sensor probe. NOTE: Sensor probe should be in the inner blue cone of the
burner flame, approximately 1/4" to 5/16" above the burner.
2. If the burner still goes off and into lockout, check the wire connections at the flame
sensor and the module board.
3. If wire connections are okay, check for continuity through the flame sensor wire.
4. If the continuity of the flame sensor wire is okay, check with microamp meter in
series with the flame sensor and flame sensor wire to be certain the flame sensor is
generating at least seven microamps within seven seconds after the burner is ignited.
Connect the meter as follows: (+) to sensor wire, (-) to sensor probe. Adjust the
position of the sensor probe, check air adjustment and check for carbon deposits on
the sensor probe if the reading is less than seven microamps.
5. When the flame sensor circuit is generating at least seven microamps, but the burner
still goes off and into lockout, replace the module board.
He might not be locking out but that 1 sec can cause the OP problem to. IMO this is past the average TT owner. It's very dangerous. The propane Company should be able to figure this out for him. Haven't heard back so maybe they have it resolved. It would be nice to let people know and check in. They might have just pick up a bad batch of propane with some moisture in it.

[wildcat_in_co]

Originally Posted by gljurczyk

Your right but you need to start some where and I would with the propane company and let them make sure no moisture is in the tanks. here is a little check list for the OP

D. Burner Ignites But Shuts Off:
1. Check to be certain that flame sensor is over slots in the main burner and that the
main burner flame is burning against the tip of the flame sensor - adjust by bending
the sensor probe. NOTE: Sensor probe should be in the inner blue cone of the
burner flame, approximately 1/4" to 5/16" above the burner.
2. If the burner still goes off and into lockout, check the wire connections at the flame
sensor and the module board.
3. If wire connections are okay, check for continuity through the flame sensor wire.
4. If the continuity of the flame sensor wire is okay, check with microamp meter in
series with the flame sensor and flame sensor wire to be certain the flame sensor is
generating at least seven microamps within seven seconds after the burner is ignited.
Connect the meter as follows: (+) to sensor wire, (-) to sensor probe. Adjust the
position of the sensor probe, check air adjustment and check for carbon deposits on
the sensor probe if the reading is less than seven microamps.
5. When the flame sensor circuit is generating at least seven microamps, but the burner
still goes off and into lockout, replace the module board.
He might not be locking out but that 1 sec can cause the OP problem to. IMO this is past the average TT owner. It's very dangerous. The propane Company should be able to figure this out for him. Haven't heard back so maybe they have it resolved. It would be nice to let people know and check in. They might have just pick up a bad batch of propane with some moisture in it.

I am not sure how big of a job it is to take the heater out and start tearing it apart to check all of these things but I am pretty sure it is more complicated than something I can do myself. Yesterday the propane people came to fill the tank and of course they didn't have a manometer with them to check it. We only had them fill the tank half way because we may be heading for Texas, but as of today it is still popping/backfiring. We are replacing the hose on the new regulator we installed a couple months ago because it had a small leak.so maybe that will help. I don't know if a small leak in the hose will cause this problem or not. The heater fires up and heats etc. It is not at the start up that it happens, it is like 7-10 minutes after it starts running that is starts to backfire. It is not a cracking noise like something expanding, it is a loud bang. I don't know if I can go buy a manometer and check the thing myself or not.

[Witch Doctor]

Originally Posted by wildcat_in_co

I am not sure how big of a job it is to take the heater out and start tearing it apart to check all of these things but I am pretty sure it is more complicated than something I can do myself. Yesterday the propane people came to fill the tank and of course they didn't have a manometer with them to check it. We only had them fill the tank half way because we may be heading for Texas, but as of today it is still popping/backfiring. We are replacing the hose on the new regulator we installed a couple months ago because it had a small leak.so maybe that will help. I don't know if a small leak in the hose will cause this problem or not. The heater fires up and heats etc. It is not at the start up that it happens, it is like 7-10 minutes after it starts running that is starts to backfire. It is not a cracking noise like something expanding, it is a loud bang. I don't know if I can go buy a manometer and check the thing myself or not.

You can take it to any propane Company on the way to Texas and have them check it. You might have found the problem if your hose was leaking didn't know that. Wondering if your leak was causing gas to build up until enough was leaked and the burner ignited it. I wouldn't be playing around with propane as you know that's very explosive gas and dangerous. Try leaving your TT door open to the furnace so it can't trap gas and see what happens. But get that leak fixed pronto.