Furnace Troubleshooting

[ScandentTrek]

Hello, all you helpful people out there.
My furnace is once again having another issue. We've been living full-time in our trailer for almost 4 years and we had 3 good years with the furnace working flawlessly. Last spring we started having trouble with it failing to ignite, and since it was almost summer I just left it. Now I'm here again because winter is coming and I need to fix it.

The furnace is a 1997 Atwood 8531-III, it's very old and they mostly don't make the parts anymore, but I've already done a replacement of the burner assembly (which was rotted to pieces) and while that fixed it for a few weeks, it's acting up again.

Here's the sequence:
I set the thermostat.
Furnace starts blowing cold air.
We smell gas.
We hear the click of the igniter - but it does not light.
Sometimes it tries multiple times, multiple clicks, sometimes it only clicks once, sometimes no click at all, but it continues to blow cold air forever without stopping. Yes, we have woken up with the air inside the same temp as outside after hours of it blowing nonstop through the night while not igniting.

When I replaced the rusted burner I was hopeful this would solve it, but alas, it has not. I'm hesitant to jump into replacing the control board because of the price, and when I did the burner replacement I visually inspected the igniter and it appeared to be fine.
However, if I understand the troubleshooting right, it seems like the igniter is at least part of the problem.
Does anyone have any experience with this furnace or a similar, older model? Thanks in advance!

[enblethen]

Thanks for the update! Stay warm!

[ScandentTrek]

Hey folks, final update. I ordered a new igniter, new solenoids for the gas valve, and a new control board (dinosaur brand). I decided to just replace all 3 parts rather than keep putting it together and taking it apart again 3 times.
Unfortunately, I broke the igniter getting it in place. The parts people only sent 1 solenoid instead of 2 and they were out of stock. So I polished up the old igniter, replaced only one out of 2 solenoids, and went on to the control board.
When I took out the old control board (which was very easy), I saw that one of the components was melted, with a bare wire sticking out the side of the melted plastic. This seems like a very Obvious sign of trouble, so I'm really glad I ordered the new one.
Once I got everything in place, I put it all back together and turned it on. It worked perfectly on the first try and has continued to work perfectly all week. Perfect timing because we just got the 1st snowfall of the season in North Idaho and my trailer is cozy and warm all night thanks to the furnace.
Thanks for your advice and help!

[ScandentTrek]

S Davis wrote:
Have the electrical connections been checked/cleaned, a grounding issue could cause those symptoms. Also when you replaced the burner did you make sure the igniter gap was set correctly? If too far you can get intermittent or no spark on some equipment.

We just replaced our converter after I spent a month troubleshooting and hunting down weird electrical issues we were having. We tried a bunch of things before going for full replacement. We went to clean the ground nut where it attached to the frame and it was so rusted it just broke off. Typical. So we have a clean and shiny new ground post attached to the frame and we followed everything back to check that it was all good. So, I'm pretty sure that is not it.
The new converter is amazing, btw. It's so much quieter, runs a lot cooler, and it won't keep burning out our LED lights every year. The replacement was easy and well worth it.

But it looks like furnace replacement is a Lot more expensive and a bigger hassle, and I don't want to do that. I'll go after the ignitor and hope that does the trick, then do the control board next. Still beats the $700 they want for a new furnace.

[ScandentTrek]

I'm going to go ahead and replace the igniter, since it's only a $30 part and fairly easy to get to.
I will hold off on replacing the control board for now, but it's going to be my next step. We just replaced our old converter and the new one is just So much better, it's really shown me what 30 years of advancement in electrical engineering can do.
I know that it shouldn't keep blowing without ignition and that it should have a set number of ignition attempts, and it's clearly not doing that, which shows me there's something wrong with the brain. You all are pretty convincing about replacing it.
We're looking to get our first snow next week, and while our electric space heater will keep us from freezing, I think a furnace is going to be Really nice to have in the North Idaho winter.

[StirCrazy]

had the same thing on mine but there were two issues, the first was it would be hard as heck to get going then once it was going it wouldn't relight reliably. that turned out to be bugs and such in the combustion area and exhaust piping that I blew out with compressed air. The second issue I had is when I replaced the blower motor it worked on the bench but when I installed it, it wouldn't light at all. turned out the board packed it in right at that time and it did exactly what you're describing. I went with a replacement from dinosaur boards

[wa8yxm]

Check the spark gap.. On mine it was a bit..er.. Wide..

One of the problems with both Atwood and Suburban is the single wire infighter flame sensor system NOTE I do not think this is your problem because when this happens it LIGHTS but shuts off you said it does not light.

IF the change over from SPARK to "Sense flame" goes wonkey.. the "Sense flame" chip which is looking for a fraction of a volt DC on the wire gets hit with about a kilovolt (1000volts) AC or about 1400 volts DC and.. Pop goes the sensor.

I had that happen (At least I think that's what happened) Ordered a replacement control board from Dinosaur boards...
First impresion (I'm trained in electronics) when I opened the box was QUALITY and upon a closer inspection right next to where I think such a sensor chip might be is a handy dandy protection device (Gas discharge tube, a kind of spike or surge supressor) Seems Dino boards thinks same as I do.

[S_Davis]

Have the electrical connections been checked/cleaned, a grounding issue could cause those symptoms. Also when you replaced the burner did you make sure the igniter gap was set correctly? If too far you can get intermittent or no spark on some equipment.

[jimh406]

I think it's the board if it is trying over and over and not igniting.

[enblethen]

I would test the two coils on the gas valve. Coils should measure close to the same resistance. Both coils must operate to get proper gas flow.
Clean the orifice on the gas valve. Soak in alcohol, do not use and type of device to clean it.