Furnace Quit - HELP!

[CindyB]

Yesterday, while camping on the Oregon Coast, the furnace in my '12 Big Country suddenly quit on the third day. It has been acting perfectly on every trip for two and a half years. Now it stopped. The fan comes on for about 30-60 seconds, then goes off without igniting the furnace. I tried shutting off the gas at the tank and purging the unit as directed in the user's manual, but the fan would not stay on long enough for the purge. Tried changing propane tanks on the theory that pressure wasn't adequate. That didn't work. There's plenty of gas getting to the cook stove, so air in the line is ruled out (I think).

Before I spend a bunch of my Alaska money going to the repair shop, I'm hoping some of you have a solution, hopefully a simple one. Is it the thermostat? I'm no mechanic by any stretch, but I can fix simple things with clear direction. A friend of mine shared that their gas furnace won't work if it gets wet somehow. Never heard of that one and it would have to squirt rain sideways to get in this furnace . . . . . well, this IS Oregon and it DID rain like a son of a gun for two days over there.

Thanks all - Cindy

 

[danemayer]

Hi CindyB,

If the blower starts, the thermostat is working. The relay between the thermostat and furnace is also working. The furnace circuit board is working at least in part.

When the blower starts, it has to get up to a certain speed to close the sail switch. That signals the furnace board that it's ok to open the gas valve and create a spark to try to light the propane.

If you stand outside while the blower starts (someone else operating the thermostat), you can probably hear the gas valve open and maybe the ignition spark. If that doesn't happen, you may have a bad sail switch or a bad control board.

It's possible to replace them yourself, but you might do better to get a mobile tech to look at it.

 

[gasman]

Make sure that the exhaust isn't blocked.

 

[Oregon_Camper]

Are you on shore power or battery power?

Does your RV have auto leveling? If so, you can get a battery voltage reading from that controller. Perhaps your batteries are not providing enough power to the heaters controller (brain) and it will in turn, not light.

 

[CindyB]

At the time, I was on 30 amp shore power.

 

[CindyB]

Okay. If this doesn't beat all. On a hunch, after a sometimes bumpy (asphalt is being repaired) ride home yesterday, just now I decided to check that furnace one more time before I take it to the shop tomorrow. I hooked up to my 20 amp house circuit, set the thermostat and it worked like a charm! Fan kept running, furnace came on. Hot air came out of the ductwork. WHAT could have caused this to not work for two days, then start working again? Did the bouncy ride knock something lose or back in place? At the campground, we were in the same place for five days, three of which the furnace worked perfectly, then quit on the 4th day and no matter what we tried, it would not start again. Even the fan would quit after 30-60 seconds. I'm thinking I should take it to the shop anyway to have it thoroughly checked out before we head to Alaska in May. What are your thoughts on this phenomenon? Is this something I should spend the money to have checked out or just chalk it up to the campground troll and leave it at that? I'm sure the repair shop will recommend bringing it in, but I trust judgments out here more. Thanks, everyone.

 

[danemayer]

Your earlier post indicated that there was good propane flow. And presumably there was nothing blocking the furnace air return inside the coach.

My best guess is that you have a problem with the furnace control board, or maybe with the sail switch, or possibly a loose connection.

A new furnace control board can be had for less than $100. So maybe as you spend $120 on labor, it may be worth throwing another $100 at the board. Once the tech is working on the furnace, changing out the sail switch will take 5-10 minutes and the switch itself is probably around $10-15.

So if the tech can't find a definitive cause, I'd suggest you have him replace the board and sail switch. In the course of replacing these parts, any loose wires will probably also be addressed.

Keep the old board as a potential spare.

 

[CindyB]

Thanks so much! Good advice.

 

[Oregon_Camper]

Your earlier post indicated that there was good propane flow. And presumably there was nothing blocking the furnace air return inside the coach.

My best guess is that you have a problem with the furnace control board, or maybe with the sail switch, or possibly a loose connection.

A new furnace control board can be had for less than $100. So maybe as you spend $120 on labor, it may be worth throwing another $100 at the board. Once the tech is working on the furnace, changing out the sail switch will take 5-10 minutes and the switch itself is probably around $10-15.

So if the tech can't find a definitive cause, I'd suggest you have him replace the board and sail switch. In the course of replacing these parts, any loose wires will probably also be addressed.

Keep the old board as a potential spare.

Dan....couldn't this also be a simple lack of voltage to heater control board, by the way of a loose connection? Then by driving home and connection might have moved enough to make a better connection? If so, I'd recommend testing the incoming voltage to the heater.

 

[danemayer]

Dan....couldn't this also be a simple lack of voltage to heater control board, by the way of a loose connection? Then by driving home and connection might have moved enough to make a better connection? If so, I'd recommend testing the incoming voltage to the heater.

Sure it could be a loose connection. But sometimes with loose connections, it can be hard to reach a definitive finding. For example, if you take off the wire nut, and it looks suspicious, can you be sure that's the cause?

I don't think I'd want to take a trip to Alaska with an intermittent furnace problem. If there's uncertainty, I think $100 in parts is cheap insurance. In fact, if it was me, considering the expense of an Alaska trip, depending on what symptoms I observed, I might throw a new gas valve and high-limit switch into the mix too.

 

[JanAndBill]

I was also going to suggest a low voltage either brought on by a park outage, or loose connection. I would first check the fuses and the screw connections there as this was a problem area on ours.

 

[kiben]

Hello,
I am also having trouble with the furnace control. A friend mentioned a similar problem with his Bighorn 3270RL, and said that it was resolved by having a tech program the thermostat. I haven't found the Dometic instructions to be as helpful as I had hoped. Any information is appreciated.
Regards,
Kiben (Kris and Ben) in Folsom, CA

 

[mlpeloquin]

Had a friend with a furnace that quit working while camping. Another one of our camping friends came over and moved all the wiring connections around. The spade connectors are tin plated and will build up an oxide layer. Once scraped off do the moveing of them the furnace worked fine. So far at least a year later it is still working in his rig.

 

[Roadventure]

So I'm a noob to all this and kicked on the furnace the other night not realizing how low my LP was. We ran out of LP, but have refilled it and reconnected it since then. The thermostat and relay clicks happen and we get 5-6 short bursts of air cycling for 3 seconds up to about a minute. Its my understanding that at this point the sail switch would be in question. I'm somewhat mechanically inclined, but am hoping not to have to take apart one of these units. Given the timing of this all, it would be great to figure this out. We are 3 days from going fulltime. Its been pretty cold lately in the NW, but in 10 days it will be in the high 90s during the day.

 

[danemayer]

So I'm a noob to all this and kicked on the furnace the other night not realizing how low my LP was. We ran out of LP, but have refilled it and reconnected it since then. The thermostat and relay clicks happen and we get 5-6 short bursts of air cycling for 3 seconds up to about a minute. Its my understanding that at this point the sail switch would be in question. I'm somewhat mechanically inclined, but am hoping not to have to take apart one of these units. Given the timing of this all, it would be great to figure this out. We are 3 days from going fulltime. Its been pretty cold lately in the NW, but in 10 days it will be in the high 90s during the day.

Hi Roadventure,

Since you ran out of propane, the first thing to check is whether you are now getting propane flow and have purged air out of the propane system. Light the burners on the range to check.

Also make sure you don't have anything blocking heat registers or the air return to the furnace. And check outside that you don't have insects or wasps building a nest in the furnace vents.

 

[Roadventure]

Hi Roadventure,

Since you ran out of propane, the first thing to check is whether you are now getting propane flow and have purged air out of the propane system. Light the burners on the range to check.

Also make sure you don't have anything blocking heat registers or the air return to the furnace. And check outside that you don't have insects or wasps building a nest in the furnace vents.

Thanks for the reply @danemayer,
I have propane flow to the stove and have been able to light just fine. I also did the bleed off trick, then turned the tank valve back to open. No registers or vents covered. The wasp thing might not be out of the question since this was in storage for 1.5 years. But the furnace did work flawlessly before we ran out of gas.

 

[danemayer]

You might find some help in the Furnace Troubleshooting Guide by Gary Brinck.

 

[Roadventure]

You might find some help in the Furnace Troubleshooting Guide by Gary Brinck.

Thanks, I already searched the forum and found the guide. Some of the system symptoms are the same but kinda a mixed bag. Letting the gas run out was probably my biggest mistake. Could a power reset help clear the board of safety errors? So if I disconnect from shore power and set my battery disconnect to off?


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[danemayer]

Ok, so when the thermostat closes, the ceiling relay clicks and the furnace blower starts. But sometimes it runs for 3 seconds or has a couple of bursts of air, and other times it runs for a minute but you get no hot air.

The intermittent blower is significant and probably not a sail switch problem. When the relay fires, 12V is supplied to the blower motor and the control board on the furnace. If the blower is intermittent, I'd check for loose connections at the furnace.

If the blower runs for a minute and the burner doesn't come on, that could be another indication that there's a problem with voltage at the furnace.

 

[Roadventure]

Ok, so when the thermostat closes, the ceiling relay clicks and the furnace blower starts. But sometimes it runs for 3 seconds or has a couple of bursts of air, and other times it runs for a minute but you get no hot air.

The intermittent blower is significant and probably not a sail switch problem. When the relay fires, 12V is supplied to the blower motor and the control board on the furnace. If the blower is intermittent, I'd check for loose connections at the furnace.

If the blower runs for a minute and the burner doesn't come on, that could be another indication that there's a problem with voltage at the furnace.

Thanks for the pointers there Dan.

Trying to pull my furnace cover off and the four corner screws for the cover plate were easy. The furnace flue cover is a bit harder. Not sure what torx T-size this is but the harbor freight cheapo T-20 is a hair under and T-25 is a hair too big. T-23 the ticket?

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