Furnace 'puffing'

[TankerIP]

Today, on a trip north, I turned on the furnace. From the inside of trailer everything seemed normal. First the fan came on, then a few seconds later, I heard the "click" I expected as the burner lit up. At first I felt warm air. From that point I thought all was normal. A minute or so later I thought I would go outside and check the exhaust. That's when I noticed the exhaust was not a continuous heat cycle , but intermittent puffs of hot would exhaust. I couldn't diagnose right then, but I wondered if it was just running a continuous ignition cycle.

When I shut the thermostat off, the unit fan ran until cool, then shut off.

Any suggestions about what I should check? I'm not sure if I have the manual on it this trip but will look a little more.

Thanks.

[overlander63]

Sounds like you may have a partial blockage, usually from mud dauber nests in the furnace.

[pmclemore]

All I know is that I don't know much. So if it were me, I'd determine whether I had plenty of gas.

Sorry, but that's it. Perhaps some of our other friends will have other ideas.

Pat

[wasagachris]

Originally Posted by overlander63

Sounds like you may have a partial blockage, usually from mud dauber nests in the furnace.

I second that idea. sounds like blocked exhaust. Can't really be sure without actually being there. Was the gas valve opening and closing or just exhaust "puffing". Did you hear the gas valve clunking open and shut and did you hear the ignitor repeatedly clicking to relight the furnace.

[TankerIP]

Here's what I have found out so far: After making the first post here I went back and lit up the furnace again.

1. I have good gas pressure. The water heater, refrigerator, and range seem to operate just fine.

2. I looked with a flash light in the exhaust and could see NO obstruction. But, would it be possible for dobbers or other critters to get deeper into the furnace area to cause problems?

3. From inside the trailer, I could not hear any "clicking" or other sounds that would indicate the intermittent attempts to light off the burner.

4. From outside, I could hear the "puffing". The exhaust smelled bad. Really like incomplete combustion/partially burned fuel. I was holding my hand about 3" from the exhaust, to feel the temperature (it was warm but not hot). I got one stronger "puff" against my hand that caused a black soot spot on the side of the trailer.

5. Actually the temp inside was not real hot like normal. So I know that while some fire is taking place it's not all burning enough to really warm the trailer.

I guess when I get home I'll have to look at it. Anyone know if it is difficult to look at and clean the combustion chamber? I'm sure you have to shut off the gas supply, but any other precautions?

[overlander63]

Originally Posted by TankerIP

I guess when I get home I'll have to look at it. Anyone know if it is difficult to look at and clean the combustion chamber? I'm sure you have to shut off the gas supply, but any other precautions?

It's pretty much disconnect the LP line, unplug the electrical connections, unscrew everything holding the furnace into the cabinetry, and slide the unit out into the trailer. IIRC, the 22CCD doesn't have any ducting, it just is direct air into the trailer.

[thecatsandi]

Spiders nest in air/gas combustion mixer?

[C Johnson]

Originally Posted by thecatsandi

Spiders nest in air/gas combustion mixer?

That's what I'm thinking too. Either that or soot/rust on the burner itself.

[SilverRanger]

I recently had a problem with the furnace in my 2005 Bambi. Intermittent ignition, incomplete combustion, but no puffing. First diagnosis, by a local RV repair shop, was debris in the orifice. They cleared it and it worked, although not perfectly, then progressively got worse until it was back where we started within 2 weeks.

Since we had the extended warranty for 14 more months, I decided to compile a short list of longstanding repair issues (furnace, A/V system, black tank flush system), and took it back to the dealership. When they took it apart, they found the burner to be rusted to the point it was beginning to disintegrate, and the ignitor to be corroded and had a hairline crack in the ceramic base. They gave back the original parts, and I found the burner just as they described (quite a mess), but the ignitor was very clean, and I couldn't find any crack in the ceramic base. It works perfectly now.

If we have the same (or similar) furnace, Atwood Everest Star 7920 II , the burner may be the problem.

Best of luck.

http://rvtruckparts.com/Image/44564.jpg

[TankerIP]

Not sure how much this will be helpful to me, but I did find a service manual for the Atwood products online:

http://bryantrv.com/docs2/docs/hflamefurn04.pdf

This manual seems to be for the 2004 and newer models but could be a resource for some older ones like mine (2002).

Interesting is the annual maintenance requirements listed in the manual. Supposed to be performed by professional RV technician, but how many folks do all those things every year?

[CanoeStream]

Originally Posted by thecatsandi

Spiders nest in air/gas combustion mixer?

This has my vote until you can rule it out. This will alter the fuel-air mix significantly.

Disassemble until you can view into the air intake and remove with a q-tip, toothpick or whatever else seems to fit.