A furnace problem that is totally new to me?? Ideas?

[Kirk]

This is especially for Gary but anyone who has an idea or possibly has seen this symptom please do jump in. On another RV forum that I am part of a new member just posted that they bought an RV with a Suburban furnace and the first time they turned it on it blew the screen off of the exhaust port when it light. They say that it seems to cycle normally but did do that a second time later. Other than telling them not to use the furnace, does anyone have any ideas of what might be the cause. I did come up with a theory but will hold off sharing that to see what someone else can suggest. This guy needs help!

 

[Gary RV_Wizard]

That appears to be some sort of explosion (back-fire) in the burner chamber or exhaust tube. The fan runs before (and after) ignition to clear out excess LP gas to prevent that, but I suppose there are faults where it could still happen. A leaky gas valve would be one possibility, but that has to be really rare. The other things that occurs to me is an obstruction in the exhaust or intake tube. The furnace is very susceptible to that sort of thing, though the usual effect is non-ignition. Insect nests, rust flakes, etc. are very common tube problems. I'd start with a through cleaning.

 

[John From Detroit]

Sounds like delayed ignition Gas/air or perhaps obstructed path... I've not seen that on RV type furnaces but on one oil fired if you tried multiple tries to fire it up it might.

I Would check the spark gap distance on the burner as a start.. NOTE: After that... I'm stumped. .

 

[Jkoht]

Did mud dobbers build an obstruction in the exhaust? I could potentially see where the reduction of the diameter of the exhaust would almost create a gun-like affect, focusing the exhaust puff into a smaller more compressed direct stream.

 

[Kirk]

The person who is asking (via internet so I have no way to look for myself) says that everything is clean and clear, but he also is new to RVs and I have no idea of his background so am not sure what to believe. Gary, your thinking is much the same as mine. The only other thing that I can think of would be if possibly too high of propane pressure could do that?? I have been working around RVs for more than 40 years and this is the first time that I have ever heard of a problem like his. The thing that seems really strange to me is that it must have closed the sail switch, unless it has failed or some previous owner bypassed it?

 

[Gary RV_Wizard]

Tough to do more than guess about probable mechanical problems that we personally cannot see or hear any symptoms. And the reports of a likely novice owner.

 

[CharlesinGA]

Too high pressure, or too low for that matter (gas that does not ignite at first then builds up enough to boom!)

If there is any possibility that this is a trailer and it has one of the recalled regulators (or one of the other brand names that is the same regulator) this this is a serious consideration.

Massive propane regulator recall

Charles