Furnace won't keep running

[lostagain]

Suburban NT 40.

At my wits end.

It starts normally, runs good for a few minutes, then the flame goes out. The Dinosaur board tries 3 times to relight like it is supposed to, then it shuts down after the fan runs for a few minutes to cool down. I have gone through everything such as the igniter/flame sensor, limit switch, sail switch, etc. The flame looks good and strong and blue. The motor runs strong. The only thing different is the propane tank got overfilled on our way down South this winter, and it seems like the trouble started after that. What if it buggered the pressure regulator at the tank? What is puzzling though, is that all the other propane appliances work fine (generator, cook stove, fridge, water heater).

So I am thinking maybe the gas valve. There are two solenoids on it. Maybe one is weak and doesn't stay open?

Or the flame sensor/electrode is bad, even though it sparks normally and I have verified that it is adjusted correctly.

The intake and exhaust aren't obstructed.

Ideas?

TIA.

JC

[Tom Y]

Is your battery voltage good? 12.25 or better?

[Gary Hatt - Publisher BCM]

Lost,

Are you in Canada or down here where the weather is above freezing?  That may or may not matter. Just asking.

It is not a Dinosaur board of it uses the 3 strikes and your out rule.  My 1967 motorhome had a 1 strike board in it and I upgraded it to a 3 strike board. It also runs after it shuts down which the old furnaces did not do.

If the other appliances work I would suspect the circuit board or the regulator on the unit.  But then again, the furnace probably draws more propane than the other devices so your tank regulator may be the problem.

We had a problem with Buck Trouts propane at the rally and someone else had a spare regulator. We swapped it out but that didn't help, but we pretty much ruled out the regulator.  If you have a friend with a spare or installed regulator I would swap it out to determine if that was the problem. Otherwise regulators are pretty cheap and you can buy one to test out. As you live where it gets a bit chilly, it never hurts to have a spare on board anyway.  You can get them in most towns pretty easy.

Otherwise you can start throwing parts at the Surburban and eventually it will probably work.

One last thing you can which is free is to try is to disconnect the line and blow air thru the line to ensure it is not blocked with crud. That is what was wrong with Buck's line. Blew a bunch of mud right out of it. This is pretty easy to do if you carry an air hose.

If you still do not get it to work, come to Pahrump this weekend and 10 of us will tell you what to do. 

[lostagain]

Thanks Gary!

We are back home, and it is still winter

I will blow out the line to the furnace. Good idea, and free.

Next I guess I could swap regulators. The one on the tank is a 2 stage. Does it have to be a 2 stage? Could overfilling the tank have pushed crud into the regulator and partially plugged it? The attendant at the gas station didn't open the spit valve and filled the tank to 100%. I wasn't paying attention, assuming he knew what he was doing... Wrong!

JC

[eagle19952]

HIGH TEMP LIMIT. May be defective and thinks it is seeing a burner box over temp....I would definitely check it.
Surely it has one...

[Dave5Cs]

My guess is air in the line. air is lighter than  LP ( thanks Jack so the air plugs up the line with an air bubble that won't move and doesn't let enough gas through to keep it lite. Open the little thumb screw on the line by where it connect to the burner if there is one. Open it a little with the gas on but switch off and bleed some out. close it let the air clear. then try to start it again. other wise it is your board. If you get a Dino board get the remote board to. You just hook it up away from the heater so it won't happen again. The heat messes with them because they are inside the unit.

Edit Lp is not lighter than air Like I originally stated. Air is lighter than LP as per Jack below informed me that was backwards. Noted and corrected above. sorry JC. But the rest is correct.

[lvmci]

Hi JC, if liquid gets to burner from over filling, it can gum up the works, propane units have to burn gas, this came from Vegas propane, after a similar problem, could affect the stove or fridge or heater, one or all, or sail switch that you already checked, tom...

[oltrunt]

Dave, I think you meant to say that propane LPG is heavier than air -- LPG has a specific gravity of 1.55 while air has a specific gravity of 1.  I'd agree with the rest of what you said.  If I miss read your meaning let me know.  Jack

[Dave5Cs]

Thanks Jack yep My bad. Thats why I keep you around Jack, LOL

[chessie4905]

make sure there are no spider webs in air intake. common problem over the years.

[Utahclaimjumper]

 Shut off all points of ignition,, then open the "spitter valve" and leave open till no liquid comes out..(only gas) Then try again.>>>Dan

[lostagain]

Thanks. Tomorrow I will try purging the gas line. I will see if there is a bleed screw. I already checked the high limit switch, so I don't think that is the problem. The tank is about half full now because we have been using the other appliances. I'll post tomorrow about my progress.

JC

[Dave5Cs]

JC heat is so over rated anyway. Tomorrow it will be 72 F  ::)why do you need heat?.. Kidding you. Say hi to the Boss for us.
Dave

[lostagain]

Well, I disconnected the gas supply line and blew it out. No crud, it was clean. I removed the regulator and took it apart. Seems clean and in good order. This afternoon, I will double check that there are no obstructions in the return air ducting, and all the vents. I have already checked the combustion intake and exhaust and they are clean.

The furnace starts normally and runs good for 5 minutes or so until it shuts down every time. Could the flame sensor be bad? But if it was, I would think it would shut off immediately after lighting, or not even light up? The igniter/sensor wire seems good, as well as the connections. I will double check that too.

Will report back later.

JC

[bobofthenorth]

There's not much for a chimney on those but is there any chance there's some kind of blockage there?