There are plenty of troubleshooting guides on the internet for rv furnaces, but what do you do after reading? You take it apart…
On a recent trip we turned on the furnace, blower ran, then within a couple minutes turned off. We had never had any trouble with it before. I did the usual thing one does, looked it up on the interwebs. The problem was I had no problem, other than it wouldn’t light.
What I have here is an “Atwood 8525-IV-DCLP L/D”, the L/D apparently means no outside access. “Less Door”? “Lost Door”? Dunno.
I had fan, I had gas solenoid clicks, I had ignition clicks, I had propane smell outside coming out the exhaust. I just didn’t have fire.
So to the local national super center for a space heater, and called it quits for trying to run the furnace for the trip. Nothing a few blankets and the space heater couldn’t handle. But it can’t stay broken.
There are two styles of rv furnace installs it appears. One where you have an access hatch where the furnace is installed from the outside, and one where there is no hatch and the furnace is installed from the inside with just an exhaust port going through the wall.
There is access to the guts of the furnace through one side of the furnace. Which is great if you can open the hatch from the outside and there it all is. In my case though I don’t have the outside access so all that stuff is conveniently pushed against the wall, under the kitchen counter. This is an outstanding place for a red LED and a sticker explaining its blinking fault patterns. Where you can’t see it.
So how does one get this thing apart?
There are 12v and thermostat wire connections, in my case I cut the 12v leaving room to splice back together, and the thermostat was wire nutted together.
So, ahem… needless to say, the gas needs to be off. The gas line is a 3/8″ flare connection, be sure to put a wrench on both sides to avoid bending anything. You won’t be able to just put a wrench on the fitting and lean on it, everything will twist up. So two 3/4″ wrenches are in order.
The exhaust port through the wall isn’t attached to the furnace to start. There is a stubby exhaust port recessed into the furnace, and a pipe that is attached to the vent leading outside, they just nest together and are not connected with any fastener.
There were 2 screws into the floor, opposite the outside wall, which were all that were holding the furnace in place fastener wise. Once these were removed I was able to pull the furnace away from the wall and off the exhaust vent. It was a snug fit. Also the exhaust for the heated air to heat the trailer was straight down, so there was some foam gasket material giving some resistance. This got it loose and out from under the sink and into the back of the truck.
Once home there were two things the furnace needed, power and fuel. I used a 12v jump pack I keep in the car to power the furnace, and a regulator/hose to a spare grill propane tank. The regulator you need to provide 11″ of water column pressure wise, and the hose needs to fit the regulator and have a 3/8″ female flare fitting on the other end. Got mine at Lowes as two separate pieces, about $30 out the door.
The last thing is the thermostat hookup. Thermostats are not complex things ultimately, they are a switch. So just wire nut the two ends together coming out of the furnace, that will tell it to be on all the time.
With the thermostat wires hooked together, once 12v is applied it will run.
I looked over this piece of shit in astonishment. These things many hundreds of dollars and they are complete junk. A single simple control board, a fan, heat exchanger which is just a winding exhaust tube, and a solenoid valve to turn the gas on/off with a burner/igniter. No sign of craftsmanship, no sign of any craps given. Hundreds of dollars…
So on the bench it did the same thing, all the clicks, all the fans, no fire.
It took a bit to figure out how to get it apart. What you have is 2/3 of the box is where the exhaust / heat exchanger lives, the fan pulls air in from the side and into the heat exchanger part of the box and in my case straight down into the floor. There are knockouts all over the box for different configurations. So the business end of it for everything is the part up against the outside wall. There you find the electronics and access to the burner/igniter/solenoid.
Here is the solenoid above the exhaust pipe, so input and output stacked up, with the fan on the left.
If you have the hardline for the gas input, which I think is the usual, you need to unscrew it from the solenoid because there it goes through a hole and captures the solenoid/burner assembly. So its just threaded in but just as with the gas connection you can’t just wrench on it, you need to support both sides. I was able to put a big crescent wrench on the solenoid assembly to hold it while putting a wrench on the hardline on the outside of the box. You have to be careful to not destroy things here, that solenoid assembly is a couple hundred bucks it appears…
Once that hardline is removed, with the furnace standing on end with the exhaust pointing up, you can unhook the electrical connections for the solenoid and igniter, take out 3 screws and lift out the whole gas assembly like you see here.
So now, hook it all back up but on top of the pile and test it. 12v to power it, and connect the thermostat wires together. Once you connect the 12v to whatever means you have, it will start to run.
If your foolish enough to try this, have a plan for how to deal with problems. Pulling the 12v will immediately turn off the gas. If you turn off the gas, it will stop burning. If the place catches fire, have a fire extinguisher. Or better yet, do not do as I did. Thats probably best.
What I found was that it would light, a tiny little bit, for a few seconds, and then it would go out. Do this 3 times 30 seconds apart or so, and then the red led on the control board would blink 3 times then pause, saying it had locked it out for failure to ignite.
The igniter was making good spark, it was lighting, just it appeared the flow of gas was no good.
Two screws hold the burner/igniter assembly on, that will expose the orifice which may need cleaning. Nope, clean as can be for me.
I then took the solenoid to a bench DC power supply, and cycled it. Seemed ok… then with the orifice out, I put compressed air gently into the valve. When the solenoid was open it was barely open. Here was the problem.
A few more cycles, I upped the amperage limit on the power supply to see if it was just not getting enough to open fully, and then one cycle it made a pop and it was wide open, not restricted at all… My solenoid had somehow stuck closed.
I know when it comes to other gas appliances like a furnace or water heater there is a common “tap the solenoid” fix for things like this. Sure enough this is what it needed.
I put it back together on top of the pile and this time… fire!
Here is a pic of the test setup. Remember, safety third as a great man once said.
Problem solved! Lets put it back together. And lets test it again before we go through all the trouble of re-installing it.
No joy. It would light but wouldn’t stay lit. It would kinda flutter out and then try again over and over. So its better but not ok now that its put back together.
Time to stand and stare at it.
One of the troubleshooting checks is if exhaust is blocked enough it won’t work. I have the exhaust port hanging off the side of the bench, can of paint counterbalancing it. No problem there.
There are two sides to the fan. One moves air from inside the trailer over the heat exchanger and out to the vents. The other side pushes air through the heat exchanger, clearing out any air/fuel mix that may explode from a failed ignition, and then providing air for combustion and pushing exhaust out when lit.
The source of air for the combustion is pulled from the same little compartment that the exhaust exits from. Normally exhaust is taken the rest of the way out through the side of the trailer so you don’t die. On the bench the exhaust doesn’t make it outside the box and… is drawn back in and is tried to be uses for combustion. This of course is counterproductive.
Ah ha! What we need is a tail pipe.
To the recycle bin, and off with the bottoms of some tomato cans, tape those together and bam. Furnace runs like a champ! I just used blue painters tape, it probably would catch fire if left to run for long. And the cans get hot. So don’t burn your garage down, and don’t burn your hand. Better yet use something not held together with tape.
Back to the RV and if it sticks again, give it a little tappy-tap-tap on the solenoid before major surgery.