# Grrr - Furnace Won't Light



## Insomniak

Just got back from a weekend trip to Julian, where it was nice on Friday and then snowed on Saturday. Not a problem if your trailer furnace is actually WORKING!! Well, it was working when we first set up, then I realized it was getting a little chilly. Got out the electric space heater, and I noticed the furnace was just blowing cold air. Ok, I'm mechanically inclined and used to spend half of my waking hours on these forums, so I thought I'd remember the fix. Nope... Everything I've tried hasn't worked.

The furnace blower comes on and the ignitor clicks, but the burner doesn't light. Both propane tanks are full, and I've tried switching between the two with no luck. The water heater, fridge and stove all work fine. Purged the propane line at the furnace and there's gas up to the connection. Put the converter into bulk mode for 14.4 volts, and no luck. Disconnected the batteries and reconnected them, nada. Even put my hand over the exhaust vent outside (as one poster did), but no burner action. Without ripping the furnace out, you can't really get at much, but the wiring connections I can see all look secure. The ducting looks like crap, and the unused vent hole covers leak air like the proverbial sieve. Tried the emergency switch overhead, and reset the remote control which was a waste of time.

The only thing unusual I can think of is that one of my kids threw her pajamas over the vent closest to the furnace to "warm them up". I don't remember if the other vents were open or not, so maybe the over-limit switch tripped and didn't reset? Even so, I'm not sure if we'd get to the point of the ignitor sparking. I'm thinking it's a gas valve problem, but if anybody has other ideas, let me know!


----------



## Dub

First thing I would do is try to see the ignitor, when you hear it clicks you should see a blue spark. No spark, just bend it to decrease the gap, I had a problem like that on my popup, closing the gap made it spark and light.


----------



## CamperAndy

Did you hear the ignitor spark?

Did you hear the gas valve open about two seconds after the ignitor started sparking?


----------



## Dub

All of my manuals have wiring diagrams with them...maybe check them to see if there is a fuse somewhere in the system that could be blown? I know that my Dometic fridge has three fuses and one blew on me last summer and wreaked havoc.


----------



## Insomniak

The ignitor is definitely sparking, you can hear it from outside at the intake and exhaust vent plate. A "clunk", then the very fast "tick,tick,tick" sound. I don't see a sight glass or any way to actually look at the ignitor or burner. I'm not sure if I can hear the gas valve opening. It's kind of hard to hear anything over the blower noise. Guess I'll pull the unit out and fiddle with it some more, or just take it in for service. It's gotta either be the gas valve or a clogged orifice somewhere.


----------



## Ridgway-Rangers

Check for carbon buildup. get a toothbrush and a can of air and clean off the ignition area.


----------



## PDX_Doug

A number of members have reported issues with a certain type of spider that likes to build nests over the orifice.
I would check for that. Carefully!

Happy Trails,
Doug


----------



## kmcfetters

I have the same problem--I am going to take the furnace completely apart over the holidays.I took it out and saw the spy glass,but didn't see it sparking. I was needing a weird wrench to break the propane line off the furnace to actually be able to open the furnace completely. I will let you know what I find next week.


----------



## Insomniak

The more I think about it, the more I feel the pajamas over the vents may have had something to do with this problem. It seems awfully coincidental that the furnace was working just fine until the vents got blocked, and an hour later we didn't have any heat. If the limit switch is malfunctioning, I wonder if it would cause these symptoms? It's an easy part to replace and only costs about ten bucks. I'll probably call Suburban and run it by them to see what they think. Sure would be nice to not have to remove the entire furnace and mess up all of Gilligan's fine vent and taping work.


----------



## Insomniak

Well, calling Suburban was a waste of time. They aren't interested in providing any information that may be useful to consumers. I guess their opinion is that most of us can barely change a light bulb, much less take apart and fix something that can potentially go "boom". All they could tell me was to "take it in for service". Guess I'll have to pull the thing out and get it bench tested somewhere...


----------



## Dub

Did you check the wiring diagram for fuses and then check them with a multimeter? And second did you actually take it apart far enough to see a spark. If the gap is not correct it will make the clicking noise but no spark.


----------



## Insomniak

Nope, haven't taken it out yet, but it's in storage. When I had it in the driveway, the farthest I got was to pull off the front cover where I saw the limit switch. Didn't see any other screws, nuts, bolts, or any other easy way to access the guts so I called it a day and pulled it back to the storage lot. I'll bring it back over after Christmas and take a closer look for this sight glass thingy, and any other way to get at the insides so I can check connections at the gas valve and circuit board. Hopefully it's something easy to fix because we're heading out again on Jan 8th for a couple of nights in the mountains. If not, at least we have the electric heaters!


----------



## Insomniak

Ok, the verdict is....a bad gas valve. More specifically, one half of the gas valve. There are two coils (like sprinkler solenoids) that are supposed to both open simultaneously and let gas flow to the burner. One lets gas into the valve and the other lets it out. The coil that lets gas out was bad. Took a couple of hours to figure it out, but that's definitely the problem - it shows an open circuit on the ohmmeter. Now to find somewhere to either buy a new coil or an entire valve assembly, which is about a hundred bucks.

Just FYI for anyone else with Suburban SF30F furnace problems, the ignitor/burner sight glass isn't easy to get at. The furnace is encased in a sheet metal enclosure that covers the glass. If you do get the furnace out of the case, the ignitor itself is to the right of the glass - if you look straight down, you may not see it sparking. To get at the ignitor, you have to remove an access cover, but also the gas line that comes out of the gas valve (use an open-end wrench). The gasket around the access cover is flimsy, so plan on replacing that as well.


----------



## kmcfetters

OK--I just had the same problem..kinda.I went out and took it all apart and was going to order the valve and decided to blow the orifice out while it was all apart.A little bit of rust came out...not much at all. But tada!! the heat is working again.Man it was a pain to take it all down just to blow some air through the line.Oh well...I'm ready to go camping now.


----------



## BullwinkleMoose

Insomniak said:


> Just got back from a weekend trip to Julian, where it was nice on Friday and then snowed on Saturday. Not a problem if your trailer furnace is actually WORKING!! Well, it was working when we first set up, then I realized it was getting a little chilly. Got out the electric space heater, and I noticed the furnace was just blowing cold air. Ok, I'm mechanically inclined and used to spend half of my waking hours on these forums, so I thought I'd remember the fix. Nope... Everything I've tried hasn't worked.
> 
> The furnace blower comes on and the ignitor clicks, but the burner doesn't light. Both propane tanks are full, and I've tried switching between the two with no luck. The water heater, fridge and stove all work fine. Purged the propane line at the furnace and there's gas up to the connection. Put the converter into bulk mode for 14.4 volts, and no luck. Disconnected the batteries and reconnected them, nada. Even put my hand over the exhaust vent outside (as one poster did), but no burner action. Without ripping the furnace out, you can't really get at much, but the wiring connections I can see all look secure. The ducting looks like crap, and the unused vent hole covers leak air like the proverbial sieve. Tried the emergency switch overhead, and reset the remote control which was a waste of time.
> 
> The only thing unusual I can think of is that one of my kids threw her pajamas over the vent closest to the furnace to "warm them up". I don't remember if the other vents were open or not, so maybe the over-limit switch tripped and didn't reset? Even so, I'm not sure if we'd get to the point of the ignitor sparking. I'm thinking it's a gas valve problem, but if anybody has other ideas, let me know!


----------



## Travis

kmcfetters said:


> OK--I just had the same problem..kinda.I went out and took it all apart and was going to order the valve and decided to blow the orifice out while it was all apart.A little bit of rust came out...not much at all. But tada!! the heat is working again.Man it was a pain to take it all down just to blow some air through the line.Oh well...I'm ready to go camping now.


Chalk another one up to rust in the 'ol gas orifice (I hate it when this happens). Probably been there since we bought the trailer, puts out more heat than ever now!


----------



## Captain

I've had this problem twice. Both times it was caused by insufficient power from the coach batteries. I attached a charger on the batteries and in no time up came the heat.
Batteries are sensitive to cold; at zero degrees, they lose half of their voltage.


----------



## kermit315

I just bought this trailer (2003 25FBS) and cannot get the heat to work. I am living in it semi permanently and it is supposed to be cold all this week. I can smell gas at the vent outside and can hear the igniters trying. Any ideas?


----------

