Furnace issues

[Jacksonrc]

Hey,

I’ve been having some furnace related issues for the last week or so.

It will come on briefly put out warm sore for a bit, then you can start to hear the ignighter fire a few times. Then it shuts off.

I took the door off and looked into the sight window as this happened. The flame starts off a perfect blue, then transitions to a yellow then an orange before shutting off.

I put in a new ignighter, it didn’t help. My next step is to go to the local supplier and get a new burner.

I have not pulled the furnace out yet....it looks to be a horrible pain to get the gas line off.

Before I do, what are your thoughts on this issue?

[chuckster57]

I think your furnace is ok. I would be looking at the regulator. Light all 3 burners on the stove and watch the flames, do they change color? JMHO but I think it may be a gas pressure/flow issue.

[Jacksonrc]

I think your furnace is ok. I would be looking at the regulator. Light all 3 burners on the stove and watch the flames, do they change color? JMHO but I think it may be a gas pressure/flow issue.

Nope, nice blue flames. I did one better too, I turned the oven on and got the water heater going. I had perfect blue flames.

[sourdough]

Don't know if it has anything to do with your issue but just something to think about;

On one occasion mine did something similar and turned out to be the control board. Only it tried to ignite, fired up for a bit, shut off then would not reignite until reset.

In November the furnace acted even more like your issue; it would come on, run for a bit but the flames would never stay on long enough for the air to get hot, just lukewarm. It would do this repeatedly but it would not warm the trailer. Turned out to be the thermostat.

Probably no bearing on your problem but something to consider "just in case".

[Jacksonrc]

Don't know if it has anything to do with your issue but just something to think about;

On one occasion mine did something similar and turned out to be the control board. Only it tried to ignite, fired up for a bit, shut off then would not reignite until reset.

In November the furnace acted even more like your issue; it would come on, run for a bit but the flames would never stay on long enough for the air to get hot, just lukewarm. It would do this repeatedly but it would not warm the trailer. Turned out to be the thermostat.

Probably no bearing on your problem but something to consider "just in case".

My new board arrived this week along with a new sail switch.. I pulled the furnace out and replaced both.

On a side note, I ordered a new high limit switch but they were out of stock and it is on back order.

After going through the purge procedures, I fired the furnace up.....took a few tries, but finally it fired and ran well for 10 mins or so. Then it shut off. Won’t come back on.

I did test the high limit switch, continuity tests just fine.

I can’t get it to fire again at all now. What’s next? Gas valve?

I’ve read a few posts about a lockout mode. Anyone know about this?

[Jacksonrc]

When i took thwbgas fitting off, there was a bit of that pipe dope (thread sealer) inside the gas line....is it possible that pipe dope is getting in the gas valve and it’s sticking closed?

How does one test the gas valve?

[chuckster57]

There should be gas compatible thread sealant on the flare fitting, can’t say I’ve ever seen a factory person put enough on to clog the valve.
We test them by turning on the furnace, then using a test light we look for voltage at the valve. Ground to the appliance and then probe the positive at the valve. IF the board and the other parts are good, the test light will light when the board sends a signal.

We use a good shop battery and a small propane cylinder with a regulator and short pigtail.

[Jacksonrc]

There should be gas compatible thread sealant on the flare fitting, can’t say I’ve ever seen a factory person put enough on to clog the valve.
We test them by turning on the furnace, then using a test light we look for voltage at the valve. Ground to the appliance and then probe the positive at the valve. IF the board and the other parts are good, the test light will light when the board sends a signal.

We use a good shop battery and a small propane cylinder with a regulator and short pigtail.


What voltage should the valve be getting?

I’ve read a few other forum posts that indicate there is a time delay relay somewhere. Where would I find it, if there is one? I can’t see anything that might be it.

[chuckster57]

Valve needs 12VDC. Delay should be built into the board if it has one.

[Jacksonrc]

Valve needs 12VDC. Delay should be built into the board if it has one.

Okay. So, IF it is getting voltage, is there a chance it is stuck shut? It’ll test it tonight.

I’m at a loss....not sure what else it could be if it’s not the gas valve.

[chuckster57]

Yes. They can stick, we tap on them sometimes. If you know it getting voltage and there is no flow then replace it.

[Jacksonrc]

Yes. They can stick, we tap on them sometimes. If you know it getting voltage and there is no flow then replace it.
So, I’m getting 12v to the valve. Still no ignition or smell of gas for that matter.

Before spending $180CDN on a valve, is it possible to double check that the valve is indeed not opening and is the problem?

[chuckster57]

Considering that the LP will flow at about 11” WC or about 1 1/2 PSI, it might be hard to verify a sticking valve solenoid. I suppose you could blow through it...

[Jacksonrc]

Considering that the LP will flow at about 11” WC or about 1 1/2 PSI, it might be hard to verify a sticking valve solenoid. I suppose you could blow through it...
Shouldn’t I at least smell the mercaptan if it is opening?

[chuckster57]

Yes you should.

[Lee]

Hi

Can you somehow tape a piece of hose... Or a straw to the valve? Then when you apply the 12v to the valve try and blow on the hose.

If the valve opens with the 12v air should pass through.

Lee

[chuckster57]

There is a plug at the bottom, and if you have a manometer you can test for gas pressure with the solenoids energized. Most RV owners don’t own the test equipment we as techs are required to have.

As long as you can verify gas pressure to the valve, but none after, then the valve has failed.

NO FLAMES or SOURCE of IGNITION present, you can loosen the line at the flare and smell for propane. Be sure to use two wrenches and tighten when done.