RV FURNACE

[fulltimeguy]

Hello all.  I have a Atwood 8535 furnace that has developed a problem over night.  It is only working occasionally.  All this started after running out of propane.  I went and had the tank refilled and now this.  I have played with it a good bit and sometimes it will cycle and other times it will not ignite. 

The fan is blowing when triggered by the thermostat.
I can't hear the the igniter at all whether it works or not.
Propane tank is full.
It heats fine when it does work.

I have swapped tank positions.  Open and closed the valves to reset them.  The stove and fridge work fine.

I have read to my eyes are blue and I haven't seen where anyone else is having it work sometimes and not others.
Any suggestions?

 

[elwood58]

Without visibly seeing the flame, it can be hard to tell if you have air or moisture in the propane line.  Set the thermostat at a level high enough to keep it running for a good long while when it does ignite, and see if that clears the issue.

 

[Gary RV_Wizard]

Since this occurred after running out of propane, odds are you have air bubbles in the branch lne that feeds the furnace. Elwood58 gave good advice on that. However, there is a chance that you sucked up oily globs when you ran the LP tank down to zero. There may be gunk (technical term!) in the bottom of the tank and a high flow appliance like the furnace can suck it right in. That will clog the burner orifice and require a cleaning. However, that sort of blockage is not usually intermittent, so if yours lights sometimes, that may not be it.

 

[Lynnszoo]

I have a 2000 dolphin motorhome. The furnace will sometimes come on and work just fine and then sometimes it won't come on at all. The thermostat is working, as you can hear it click at the current temp, but nothing else happens. Please help want to get on the road.

 

[John From Detroit]

Gary. Think about that air bubbles line.. With a Fridge yes. But the Furnace sucks enough propane on the first of 3 tries that if there was any air in the line there is no more. and it tries 3 times before lockout.

I had an overly large spark gap and I've read of clogged gas jets.

 

[Rene T]

Keep in mind that This is a 5 year old post but it still may be helpful for someone

 

[Lynnszoo]

Keep in mind that This is a 5 year old post but it still may be helpful for someone

It never even gets to that point. The blower dies not come on.

 

[Lynnszoo]

Gary. Think about that air bubbles line.. With a Fridge yes. But the Furnace sucks enough propane on the first of 3 tries that if there was any air in the line there is no more. and it tries 3 times before lockout.

I had an overly large spark gap and I've read of clogged gas jets.

It never gets to that point, the blower never starts.

 

[Gary RV_Wizard]

I have a 2000 dolphin motorhome. The furnace will sometimes come on and work just fine and then sometimes it won't come on at all. The thermostat is working, as you can hear it click at the current temp, but nothing else happens. Please help want to get on the road.

RV LP furnaces are very sensitive to the air/fuel mixture, so even a tiny disruption in the air intake or exhaust tubes can cause ignition failure. I'd start by thorughly cleaning the tubes that go out thru the sidewall to remove dirt, rust flakes, cobwebs, etc. Try a vacuum cleaner first, but sometimes it has to be disassembled for cleaning.

 

[Lynnszoo]

RV LP furnaces are very sensitive to the air/fuel mixture, so even a tiny disruption in the air intake or exhaust tubes can cause ignition failure. I'd start by thorughly cleaning the tubes that go out thru the sidewall to remove dirt, rust flakes, cobwebs, etc. Try a vacuum cleaner first, but sometimes it has to be disassembled for cleaning.

The main problem is that not even the blower comes on which must happen before the sail switch will allow it to light.

 

[Charlie 5320]

All the thermostat is, is a switch. When there is a call for heat the stat makes a path, power from the R terminal to the W terminal on the furnace control board. Now IF the stat is bad, it may NOT pass full power to the W terminal on the board. You will need a meter that will read DC voltage to trouble shoot this problem. Turn the stat to call for heat, take a reading on the W terminal on the board to ground, should be 12 v plus. IF it is less, there may NOT be enough power to make the relay on the board.

 

[Gary RV_Wizard]

The main problem is that not even the blower comes on which must happen before the sail switch will allow it to light.

OK. You originally said it will not ignite at times, so I was looking at that perspective. You also said it works sometimes, so the problem seems intermittent as well.

There are three possibilities If the fan doesn't start reliably:

1. Thermostat "heat needed" signal isn't reaching the furnace every time
2. Furnace 12v power source is intermittent
3. Faulty wire connections at furnace so power or heat demand signal gets lost.

 

[Lynnszoo]

I opened up the outside access panel. Please understand we are the second owners. I found everything covered in a thick layer of dust laying in a bed of dead bugs. The circuit board was placed in a baggie (open on top)and tucked into the left side behind the motor.

I cleaned everything out and off, used a toothbrush to help me clean the cuecuit board that was covered in dust and she is working fine now.

 

[Gary RV_Wizard]

Thanks for the feedback - it's always helpful to learn the nature of the problem (for future reference!).