Atwood Furnace Problems

[pomology]

I have a problem with the Atwood furnace on my 5th wheel (2019 Montana High Country )

I just bought the unit second-hand six months old from a private seller and have never used the furnace system before. (The person I bought it from never used the furnace either because they had free electricity at the RV park). When I turn up the thermostat and go outside, the furnace blower turns on, and the sparker clicks to ignite gas. I smell pretty strong gas exiting the exhaust pipe and actually hear the flame briefly ignite for ½ second or so, and feel a brief rush of hot air. Then the flame goes out. The sparker attempts to re-ignite, I feel a rush of heat for a ½ second, and then the flame goes out. This happens repeatedly over and over again until the unit finally times out and the red LED has the 3-blink pattern.

Things I've tried:

1) All the other propane appliances work. Stove works fine, gas water heater (which is right beside the furnace) also works perfectly.

2) Propane tanks are full.

Any ideas of what I should try next would be much appreciated!

Thank you!
Randy

[DFord]

cbr46 wrote:
I had muddobber babies INSIDE the gas suppy tube. How they got through the gas jet I don't know but they were clogging the jet.

Like you, I don't know how they're able to get inside there but it happens pretty often. The screens will keep the adults from getting in there to build nests and lay eggs. Spiders love to build a web across the hole in the orifice too.

It sure looks like they were awful busy bringing all that mud in. Cleaning it up is no fun.

[cbr46]

I had muddobber babies INSIDE the gas suppy tube. How they got through the gas jet I don't know but they were clogging the jet.



I also had a pretty good mess inside the combustion chamber.



Good luck,
- bob

[marc71]

So I’m having the same problem as the OP was having... I have replaced the circuit board, sail switch and igniter... I also replaced the gas regulator, nothing to do with the heat issue just didn’t like the one that was on there. It’s an Atwood 8535. I took the screen part out where the gas flowes through, there was some rust blocking a few places, wire brush cleared that up. I put everything back together and still having the same problem... fan comes on, igniter lights and the heat blows briefly and kicks off, repeats two more times and shuts down, light blinking 3 times. I don’t know what else it could be??

[pushtoy_2]

my MH did that the circuit board got wet.. the vents on the out side were facing the wrong way and letting water in

[cbr46]

I have a similar problem. My furnace is 17 yrs old. Some surface rust but overall pretty clean.

Fan comes on, a minute or so later gas is turned on and I can hear the igniter.
I can faintly smell propane coming out the furnace exhaust. Faintly. It comes & goes.
Sometimes the furnace will light but then goes out. I can hear a 'woof' or two . . . or multiples.
Sometimes it will run for a few minutes but never reaches a good outlet temp. Maybe 90F. It should be 120F+.

There were muddobber nests inside the flame chamber. They were cleaned out. Otherwise the inside was pretty clean.

The burner was removed and although it looked pretty clean I ran a quick wire brush on it (by hand). I also inserted a rubber coated wire into the gas jet. It went in easily telling me the jet wasn't clogged. I didn't remove the jet for more inspection.

Q1 - Control board, gas valve or rust inside the supply tube (clogging the gas jet)? #1 I don't want to spend $90 for a board I may not need and # 2 it's not exactly easy to disassemble (the supply tube nut is so tight I disassemble the fan shroud to get it out).

Q2 - Can I apply 12V to the gas valve to actuate it? For testing ONLY!

Thanks,
- bob

[dougrainer]

IF under warranty, I would ask that the furnace be replaced. RUST is NOT a problem on Furnaces where you had rust. On a 2019, that is NOT right at all. Doug

[pomology]

Hello Friends!
First please pardon this very tardy reply. Second I REALLY appreciate every reply above. They really helped me. Your input allowed me to fix the problem, here’s how I did it:

So I took the burner out of the unit and immediately saw the problem. The burner “grate” ( not sure the official word - it’s the screen-like part, filled with tiny holes) appeared to be completely rusted. It was rather soft, and could be brushed off with some effort with a toothbrush, almost like orange hard caked mud. Every hole was plugged with this stuff. It did also appear there had been water in the unit as the inner side of the exhaust port where the burner is inserted, clearly had rust streaks where it looks like water was in the unit and drained out of the inside of the exhaust port into the bottom of the furnace.I saw a little corrosion on the back of the electronic logic board. Also when I disconnected the gas line, several drops of water ( not oil!) dropped out of the gas line! So I brushed off all the rust , put everything back together and it started right up! For about 15 minutes it was constantly burning for 10 or 20 seconds, then going out , relighting, and burning 15 or 20 seconds more, over and over and over. I’m guessing that maybe there was water in the line that needed to get eliminated? Anyway, after about 30 min, the unit stopped having to relight intermittently and now runs perfect. As for why water could have gotten in the unit i checked after a rainstorm and indeed there was water on the bottom of the unit as well as on the shelf in the middle of the unit. At first I couldn’t tell where it could possibly come from, but then I saw that the silicone caulking around the edges of the outside of the unit had a couple small cracks in it at the top of the unit , apparently allowing rain to enter. I re caulked and will check for any more water after the next rain.

Thank you again everyone, your input helped me so much!
Randy

[almcguire]

pomology wrote:
I have a problem with the Atwood furnace on my 5th wheel (2019 Montana High Country )

I just bought the unit second-hand six months old from a private seller and have never used the furnace system before. (The person I bought it from never used the furnace either because they had free electricity at the RV park). When I turn up the thermostat and go outside, the furnace blower turns on, and the sparker clicks to ignite gas. I smell pretty strong gas exiting the exhaust pipe and actually hear the flame briefly ignite for ½ second or so, and feel a brief rush of hot air. Then the flame goes out. The sparker attempts to re-ignite, I feel a rush of heat for a ½ second, and then the flame goes out. This happens repeatedly over and over again until the unit finally times out and the red LED has the 3-blink pattern.

Things I've tried:

1) All the other propane appliances work. Stove works fine, gas water heater (which is right beside the furnace) also works perfectly.

2) Propane tanks are full.

Any ideas of what I should try next would be much appreciated!

Thank you!
Randy

Randy
The unit is not sensing flame. Electrode 10% board 90%. Call Dometic customer service and have the model and serial of the furnace and need a replacement Board.

[dougrainer]

If you hear the spark and smell LP and sometimes you feel heat, the Spark Electrode is to CLOSE to the burner. You will have to have the furnace pulled and the Spark Electrode gap set. 2019, the furnace is under warranty. Makes no difference you are the 2nd owner. Just find a service center that will do Atwood/Dometic warranty. Doug

[maillemaker]

The blower runs constantly for several minutes, with the sparker attempting to light every few seconds through that time period. It's like the flame just flickers in there before going out every time. I feel a burst of heat and that hollow "whooshing" sound that happens when the flame ignites, only for it to immediately go out. Only after several minutes does my unit go into lockout mode.

Yup, this is all typical fail-safe stuff. When you turn on the furnace, the first thing that happens is the blower motor is turned on. Inside the furnace there is a "sail switch" that blows in the wind made by the fan. If that switch does not activate, it tells the furnace controller that the fan isn't running, and it's not safe to fire up the furnace with no airflow (it would burn up). That is check number one.

Then it opens the gas valve and fires the ignitor. If it doesn't detect a flame, it will shut things down. It will try to re-start some amount of tries before it gives up (lock out).

As others have said, either you have a bad control board, or a poor electrical connection to the flame sensor, or there is debris in the furnace causing poor gas flow and making the flame extinguish.

When you open the cover to the furnace on the outside of the RV you should see the burner inlet pipe with the ignitor. Sometimes there are two prongs - one for the spark and one is the flame sensor. Other furnaces combine both into one prong. Make sure the prongs are rust and debris free.

If you remove the bracket holding the ignitor assembly you can usually stick a vacuum pipe up the inlet pipe and suck out any debris down there. Make sure the heater is cold first of course.

[badsix]

2x above ^^^
Jay D.

[joebedford]

My furnace used to do that until I tightened all the push on spade connectors.

[A1RVTraveler]

You need to pull the furnace and inspect the burner, LP orifice and igniter. I suspect you have a bug in the LP orifice or a mud dauber nest in the burner area. This is a common problem.

[pomology]

Thanks. The blower runs constantly for several minutes, with the sparker attempting to light every few seconds through that time period. It's like the flame just flickers in there before going out every time. I feel a burst of heat and that hollow "whooshing" sound that happens when the flame ignites, only for it to immediately go out. Only after several minutes does my unit go into lockout mode.

I'll clean all the connections today and report back.