Atwood furnace help

[Mobilegreg65]

I have an older atwood 8525-III that won't ignite. I have replaced the thermostat, circuit board, gas valve, electrode and LP pressure regulator. The system will start with fan, you can heard the click of the gas valve then the clicking of the electrode but no ignition. I have a full LP tank and all other gas appliances work fine. What am I missing? I did a kit a few years ago that included a new burner and it still looks good.

 

[failsafe503]

Does your board have an LED on it? That will give you a code you can help diagnose your problem

 

[TJ&LadyDi]

It sounds like everything in the ignition circuit is working, so lack of gas flow is suspect. The fact that other propane appliances indicates that gas is flowing to those points. You could have a buildup of fluid in the supply lines blocking gas flow to the furnace. Propane can leave an oily residue that can gather in a low spot in the supply lines and block gas flow.

Blowing out the supply lines with compressed air can resolve the problem, but it can be a messy job. You need to remove the supply line at the furnace and provide some kind of a container to collect the fluid (a 2-liter pop bottle with the supply line routed inside and loosely taped in place, perhaps?).

TJ

 

[failsafe503]

I also just read this interesting bit from another person with the same problem:

(from blinking diagnostic error on Atwood 7916 furnace )

"I finally got around to fixing the problem. I tried a variety of things:
- Removed the sparker and tested it. Worked fine...strong spark.
- Adjusted the stove's gas regulator 2 stops out, then 2 stops in, just because I read somewhere that it fixed someone's problem before. Didn't help me.
- Checked the anticipator in the thermostat. I realize that it sounds weird that it would have anything to do with the problem, but someone with the exact same symptoms as mine swears that adjusting it fixed his problem. My anticipator was set almost to zero, which was weird since it's supposed to be above the .48 mark. So I set it to betwen .48 and 1. But like I said, it didn't help.
- Removed furnace valve and peered through the port and the valve body. Looked fine.
- Removed burner unit and cleaned out 2 or 3 of the holes in the mesh since they had some junk in them.
- Cleaned out the flame chamber...there was a large bumble bee carcass in there.
- Put an air hose in the chamber and blew out the ducting.
- Inspected the vent port on the outside of the trailer.
- Had the sparker / sensor unit tested at an RV shop.
- Had the controller board tested at an RV shop.

None of the above fixed the problem. So then I decided to adjust the main pressure regulator. I turned it clockwise 2-3 full turns. That caused the furnace to start more frequently, but still not consistently. It did, however, result in a slight change.

Before, the symptoms were:
1. Turn on the furnace switch.
2. Blower runs for 15 or so seconds.
3. Gas flows (I know there's gas flowing because I can smell it).
4. Igniter starts sparking continuously for about 3 seconds.
5. Furnace doesn't light. After 15 seconds, repeat steps 3 & 4, then repeat 3 &4 again.
6. Flash the LED error code.
7. Blower shuts down after 15 seconds.

Now, after adjusting the pressure regulator, the steps are the same as above except:
4. Igniter starts sparking and stops after maybe 1/4 seconds. I can hear a pop, like the gas lit and then went out. Then the sparking continues with maybe another pop and pause in the sparking. Other times, it catches and stays lit. But usually on the 2nd or 3rd sparking cycle.

So basically, it's more likely to start after adjusting the pressure regulator. Thinking that I was on the right track, I built a manometer, hooked it up to the fridge's gas line, and then tested the pressure.

With the 2 stove burners on maximum, and the furnace running (it just happened to run for my test), the manometer showed 9 inches of water. The proper pressure with those appliances on should be around 11 inches. So I turned the pressure regulator adjuster clockwise several times (6 or so) until it was at 11 inches. Then I shut down the furnace and stove. With all the appliances turned off, the pressure rose to 12.5 inches. That was good, because the requirement is that it not go above 14 inches.

When I tested the furnace after the adjustment, the furnace lit within a tiny fraction of a second after the igniter starter sparking. And it did this very consistently, always on the very first spark cycle.

I never suspected that the gas supply could be the problem since our fridge and stove worked fine. But I guess the problem with the furnace is that it has a very wide burn area (ie: there's not a single, narrow point of flame) so there just wasn't a high enough concentration of propane finding its way to the sparker during the furnace lighting cycle...plus the chamber is being vigorously ventilated by the blower.

So, for anyone who has this problem (and I've seen it several times on the web), check your gas pressure, first. It could save you a lot of trouble."