Propane Furnace Won't Fire

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Propane Furnace Won't Fire

December 08, 2011, 11:24:40 am

The forward Atwood furnace failed on our recent trip. Symptoms were: blower runs; I can hear a click which I think is the propane valve; I can smell propane at the exhaust for each of three attempts to start; blower continues to run, but system doesn't try to start again.

The rear furnace works well, the stove works well, the refrigerator worked well until the cooling unit ruptured. That's a story for another thread. The new cooling unit is here. I'll see if I can put it in.

I put a new Dinosaur control board in the furnace. The fan starts, I can hear the propane valve open, I can smell a puff of raw gas, I think I can hear the sparker, but there is no ignition.

I think someone had a similar experience and found that the regulated gas pressure was low. Are there other things to check? Where would I get an appropriate regulator? How would I check the pressure?

I plan to be at FOT on Monday, but I haven't checked to see if they can work on the furnace.

Re: Propane Furnace Won't Fire

Reply #1 – December 08, 2011, 11:38:29 am

Yes, check gas pressure with a manometer. But, if the propane regulator is OE, probably a good idea to replace it anyway-- around $25. be sure the replacement is the correct one-- the vent (quarter size screen) points DOWN. So it will either be in line with or perpendicular to the long axis of the regulator depending on whether the regulator is installed horizontal or vertical.

Also possible that rust or a dirt dobber nest is blocking the ignitor.

Brett

Re: Propane Furnace Won't Fire

Reply #2 – December 08, 2011, 11:51:27 am

Had the same thing, turned out to be a plugged orifice. Fix is simple unscrew the gas line to the burner at the control valve. Using coach compressed air blow air into the line, the plug should free and pass thru small hole.

Re: Propane Furnace Won't Fire

Reply #3 – December 08, 2011, 07:27:08 pm

I am having intermittent failure of the forward Atwood propane furnace on the U225. It will come on and heat up the coach nicely but then, at some point later, will stop igniting and simply blow cold air for, apparently, ever.

The first time this happened was the first night we had the coach. I noticed that the vents were blowing cold air so I shut off the furnace, left it off for an hour or so, and then started it again and it worked fine.

It continued to work okay until this afternoon when the same thing happened. I have it shut off now and will go back and see if it will start. However earlier attempts to restart it failed (simply blew cold air). I haven't been able to hear any "clicks" but my hearing is nothing great and I'll have to wait for the DW to come home from work.

Intermittent problems are fun... but often turn out, eventually, to be intermittent no longer.

Craig

Re: Propane Furnace Won't Fire

Reply #4 – December 08, 2011, 07:30:56 pm

Craig,

First thing to check with your symptoms is voltage at the heater. If insufficient voltage, fan speed is too low to close the sail switch. If the sail switch doesn't close, no ignition and no propane valve opening.

Did this happen with the coach plugged in(i.e. converter providing power)?

Brett

Re: Propane Furnace Won't Fire

Reply #5 – December 08, 2011, 07:34:45 pm

These fans use up mega amps of power. The quickest way to dischrge a battery is to run the furnace unplugged. Make sure you are plugged into power and that the batteries are charging properly. The multimeter is your friend.

Re: Propane Furnace Won't Fire

Reply #6 – December 08, 2011, 07:47:26 pm

I am sure Peter is taking about plugged into shore power. That way, the converter or inverter/charger will keep battery voltage up, so the fan spins faster, so the sail switch stays closed and the furnace stays running.

Could other things cause these symptoms-- YES. But check the easy, most likely, least expensive one first.

Brett

Re: Propane Furnace Won't Fire

Reply #7 – December 08, 2011, 07:53:01 pm

Quote

I am sure Peter is taking about plugged into shore power.

Yup...Sorry for the lack of clarity...

Re: Propane Furnace Won't Fire

Reply #8 – December 08, 2011, 08:18:58 pm

Quote from: wolfe10 – December 08, 2011, 07:30:56 pm

Craig,

First thing to check with your symptoms is voltage at the heater. If insufficient voltage, fan speed is too low to close the sail switch. If the sail switch doesn't close, no ignition and no propane valve opening.

Did this happen with the coach plugged in(i.e. converter providing power)?

Yes, the coach is plugged in to 50-amp service and all lights are green. The fan seems to have plenty of speed (and output - cold air, of course). Battery voltage reads 13.49 vdc. I have not tried to measure the voltage at the front unit however. Access is difficult.

The rear furnace goes through its operating sequence (fan, then ignition, then operation, then ignitions stops, and then fan stops) with no problems.

I tried the front furnace with the rear unit turned off completely to see if it was a low-flow situation but no change. Tonight letting it sit is not fixing the problem either.

I notice two valves on the propane tank. One on top of the other. The top one was open all the way and the bottom one is closed all the way. Looked for something pertinent to this in the manuals but didn't find anything.

After dinner the DW and I are going back to see if she can her the click of the propane valve opening. If the valve operates then the next step will be getting in to measure voltages at the unit. I suspect it might be a partially clogged line, however. Getting the line to the point where it can be flushed with air is going to be fun.

Craig

Re: Propane Furnace Won't Fire

Reply #9 – December 08, 2011, 09:02:24 pm

If your voltage dropped way down, the detector may have shut off the propane. Do your burners light on the stove? Do they have a full flame? Regulator could be bad. New upgrade to a 2 stage regulator is less than $20. Available at any trailer or RV store. Call around for best price. I replaced mine as it had a small leak. You do have propane in the tank?

If you replace the regulator, the 2 stage is about an inch longer than the original. I had to add a strap (for vibration) and use a big crescent wrench to rotate a fitting a few degrees but easy job. PM if you need to replace regulator as I have detailed photos of the new installation.

Re: Propane Furnace Won't Fire

Reply #10 – December 08, 2011, 10:02:01 pm

Craig,

The upper propane tank valve will be VAPOR and will go through the house regulator and the solenoid controlled by the propane detector.

The lower propane tank valve will be LIQUID and will go to the liquid propane generator.

This is how it came from Foretravel. Many of us have switched our generators to high pressure vapor and sealed off the vapor tap.

The furnace operates as do all other house based propane appliances off the vapor port. So it must be open.

Checking voltage at the front furnace isn't that difficult. Open the outside access door (two standard screws) and check voltage with the furnace fan running where the positive and ground wire attach to the furnace wiring.

Also, check that all inside vents from the furnace are open and that the ducts under the couch are not off, crushed, etc.

Sure, it could be something else, but start with the free stuff.

Brett

On edit: I was asked by PM what I meant by switching the generator to high pressure vapor and capping the liquid port. Please see: 6.5 Onan hard to start also

Re: Propane Furnace Won't Fire

Reply #11 – December 08, 2011, 11:28:25 pm

Ok... so upper valve is on. The rear furnace works fine. When I turn the switch on the thermostat to "on" the front furnace fan comes on (after about 30 seconds) and just stays on blowing cold air. We cannot hear any valves "clicking" (but we can on the rear one). When I turn the switch to "off" the fan stays on for about 30 seconds then shuts off. No "clicking" sounds.

Meanwhile, the rear furnace is working away just fine. I assume that the propane leak detector would shut down all the propane appliances including the rear heater.

The fact that I cannot hear the valve open or close makes me wonder what is up there, too.

Craig

Re: Propane Furnace Won't Fire

Reply #12 – December 08, 2011, 11:53:22 pm

Craig,

With fan running, but no propane valve clicking open (you would also smell propane at the furnace exhaust) and no "click, click, click" of the ignitor, the first suspect is that the sail switch is not closing. Reasons for that include: low voltage at the furnace (fan turning too slowly), restriction in the air return (unlikely unless something has fallen into it under the sofa), crushed heater duct or closed heater outlets. Of course, it could be the sail switch itself or even a PC board. But as discussed, check for air flow restrictions and voltage at the furnace. I have seen furnaces that had a poor ground path give these symptoms.

Brett

Re: Propane Furnace Won't Fire

Reply #13 – December 09, 2011, 12:06:00 am

The fan is going great guns and putting out copious quantities of (very cold) air. I think the sail switch is a likely culprit and that would also be the type of switch that I'd expect to work intermittently until it finally failed completely.

I wonder if we can still get parts for these things. The service center manual shows a dealer in Moses Lake and I'm pretty sure I know which outfit that is so I'll try them tomorrow.

It's certainly not propane... all four burners on the stove work without a flicker and the rear furnace cycles on and off just fine. Previous owner claims not to know anything but that is entirely possible since it worked fine for me for a while, too.

In the meantime I turned the rear thermostat up to 60 and that should hold the coach 'til I can get an idea of whether I can replace the sail switch.

Thanks for everything... I'm going to bed.

Craig

Re: Propane Furnace Won't Fire

Reply #14 – December 09, 2011, 08:38:41 am

Craig, Open the outside furnace hatch and pull the off the connectore to the board, clean up the contacts and then reinstall it. I know, sound silly but on mine I have to do this about every other winter.
Gary B

Re: Propane Furnace Won't Fire

Reply #15 – December 09, 2011, 10:28:11 am

Quote from: Gary Bouland – December 09, 2011, 08:38:41 am

Craig, Open the outside furnace hatch and pull the off the connectore to the board, clean up the contacts and then reinstall it. I know, sound silly but on mine I have to do this about every other winter.
Gary B

Not silly, have to do the same to mine, HW heater also. Check obstructions to sail switch. Rodents can get in there also. Would download a PDF of your furnace and go through their TS check list. You probably have one, but a digital voltmeter and a lighted probe comes in handy when troubleshooting. Do search for other forums that have furnace topics.

Pierce

Re: Propane Furnace Won't Fire

Reply #16 – December 09, 2011, 08:20:20 pm

Where is the sail switch? Is there a way to get the orifice out without pulling the furnace?

I replaced the ignitor board and still have no joy. The fan runs great and moves plenty of air through the ducts and the burner chamber. I can hear the propane valve open for three tries. I can smell propane at the exhaust when the valve opens. I can hear the sparker. There is not ignition. I suspect debris somewhere in the orifice or burner. All other appliances are working properly.

It looks like pulling the furnace includes disconnecting several ducts which are virtually inaccessible without some deconstruction. I loosened the nut for the propane connection, but was not able to pull the line out of the furnace housing.

Re: Propane Furnace Won't Fire

Reply #17 – December 09, 2011, 09:23:03 pm

Quote from: Gary Bouland – December 09, 2011, 08:38:41 am

Craig, Open the outside furnace hatch and pull the off the connectore to the board, clean up the contacts and then reinstall it. I know, sound silly but on mine I have to do this about every other winter.
Gary B

Today I went over to the RV and took off all electrical connections and cleaned them the best I could. Some of them are not easily cleanable (both ends inside housings) and those I connected and disconnected several times. Then I went in the coach to turn on the furnace and went back out to measure voltages. Just as I was starting to measure the main voltage at the circuit breaker the furnace ignited and started heating.

I'm going to go over in a bit and see if it's still working.

Craig

Re: Propane Furnace Won't Fire

Reply #18 – December 09, 2011, 10:02:11 pm

Quote from: J. D. Stevens – December 09, 2011, 08:20:20 pm

Where is the sail switch? Is there a way to get the orifice out without pulling the furnace?

I replaced the ignitor board and still have no joy. The fan runs great and moves plenty of air through the ducts and the burner chamber. I can hear the propane valve open for three tries. I can smell propane at the exhaust when the valve opens. I can hear the sparker. There is not ignition. I suspect debris somewhere in the orifice or burner. All other appliances are working properly.

It looks like pulling the furnace includes disconnecting several ducts which are virtually inaccessible without some deconstruction. I loosened the nut for the propane connection, but was not able to pull the line out of the furnace housing.

On my old furnace in my bus, the sail switch was easily accessible just before the combustion chamber. Not sure exactly where ours is located. If you smell propane and can hear the sparker, the mixture may not be within the combustible range due to mud from insects or other debris on or around the orifice. Propane does not have a large flammable range so if the mixture is not right on when it passes the "sparker", it won't light.

Pierce

Re: Propane Furnace Won't Fire

Reply #19 – December 09, 2011, 10:08:20 pm

Quote from: J. D. Stevens – December 09, 2011, 08:20:20 pm

Where is the sail switch? Is there a way to get the orifice out without pulling the furnace?

I replaced the ignitor board and still have no joy. The fan runs great and moves plenty of air through the ducts and the burner chamber. I can hear the propane valve open for three tries. I can smell propane at the exhaust when the valve opens. I can hear the sparker. There is not ignition. I suspect debris somewhere in the orifice or burner. All other appliances are working properly.

It looks like pulling the furnace includes disconnecting several ducts which are virtually inaccessible without some deconstruction. I loosened the nut for the propane connection, but was not able to pull the line out of the furnace housing.

Your sail switch is fine. Were it not functioning, it would not signal the PC board which would not open the propane valve or trigger the ignitor. Likewise I suspect debris in the combustion chamber. Not a high chance of success, but you have nothing to loose by shooting compressed air into the air intake and/or exhaust (from outside of coach).

Re: Propane Furnace Won't Fire

Reply #20 – December 09, 2011, 11:37:07 pm

You might take a stiff piece of wire and run it in and through the burner tube and see whether or not a mud dauber wasp built a nest inside there.

Re: Propane Furnace Won't Fire

Reply #21 – December 10, 2011, 12:13:37 am

Thanks for the additional information.

The furnace fired and ran for a while this evening. I shut it down, and it would not fire again.

The daubers have been in there. I was able to knock out a couple of pods with a screw driver. Getting into the combustion chamber appears to be a challenge. I'll see what I can do with a coat hanger and some compressed air. The exhaust tube is easy to remove. Getting full access to the combustion chamber is a challenge. Would water cause problems? On our previous coach, the water heater was rendered dysfunctional by dauber nests. We took it to an RV repair shop and they managed to clean our the heating tube with water. Could I do something similar on the furnace? I doubt it, but perhaps sometime has tried it.

I have added screen, but damage has been done. The furnace is right on the edge of functionality. We plan to go north for the holidays, and having two functional furnaces is important.

I send thanks for the suggestions. We may be able to bring the furnace back to life.

Re: Propane Furnace Won't Fire

Reply #22 – December 10, 2011, 01:01:17 am

Well.. so far, so good on my front furnace. It was still firing and keeping things warm so I'll keep my fingers crossed that the problem is solved for now.

Thanks to everyone for the suggestions and advice. This forum is truly an amazing resource.

Craig

Re: Propane Furnace Won't Fire

Reply #23 – December 10, 2011, 01:26:40 am

Suspect no water damage unless you mean corrosion on connections. Would focus on orifice/jet area with what ever you can get in there. Would also make sure all electrical connections are really clean.

Some furnaces have a small screw that holds a sliding sleeve in place at the burner. The sleeve controls the air/fuel mix. If it comes loose, it can move causing difficult ignition, inefficient use of fuel and if it goes too rich, the production of CO. Our furnaces seem to produce almost as much heat out their exhaust as heat in the coach so it's nice to know they are working at their best. Mentioned the sleeve as foreign object used to clean the area could possibly loosen/move it but hopefully not.

Good to have 100 percent confidence in furnace if going up to real cold. I think it's cold here in the 20's.

I have had several other RV furnaces out and fixed them pretty easily but not ours yet. Rear stateroom squirrel cage make a little ticking noise but low on priority list.

Craig, good work!

Re: Propane Furnace Won't Fire

Reply #24 – December 10, 2011, 09:07:06 am

That's good news for Craig. I expect a bit of dielectric grease on the electrical connections might cut down on corrosion and lengthen the maintenance window for the connectors.

Quote from: Pierce & Gaylie Stewart – December 10, 2011, 01:26:40 am

Suspect no water damage unless you mean corrosion on connections.

My question about water damaging the system was a question about whether I might cause damage by trying to flush out debris with water. I saw it done with good success to clean dauber nests from a water heater. I may flush with water based on the old advice: "If jams, force it. If it breaks, it needed to be fixed anyway."

Quote

Some furnaces have a small screw that holds a sliding sleeve in place at the burner. The sleeve controls the air/fuel mix. If it comes loose, it can move causing difficult ignition, inefficient use of fuel and if it goes too rich, the production of CO. Our furnaces seem to produce almost as much heat out their exhaust as heat in the coach so it's nice to know they are working at their best. Mentioned the sleeve as foreign object used to clean the area could possibly loosen/move it but hopefully not.

We have such a sleeve on the water heater. I have adjusted those for least noise while maintaining a clean, blue flame. I don't think there is such an adjustment in the Atwood furnace.

Quote

Good to have 100 percent confidence in furnace if going up to real cold. I think it's cold here in the 20's.

Last year we remained comfortable during several days below 10F as a high temperature. We bought the FT to deal with such conditions after a less successful adventure in SOB.

At home in Texas, we think it's cold at 40F.

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