Stumped by Furnace Issues

[Gordan D]

Lookjng for ideas. When we turn the furnace on it cycles thru and functions properly. It will work fine several times and then it will turn on, the fan will run, but it won't ignite. Just blows cold air. We've replaced the sail switch, the circuit board and the temp sensor. It still does the same thing after replacing these parts. I have no clue where to look next. It seems to be intermittent as it works fine a couple of times and then fails. Anyone have any ideas on what else I can check? Help is greatly appreciated.

Camper is a 2018 Laredo 325RL.

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Originally Posted by Gordan D

Lookjng for ideas. When we turn the furnace on it cycles thru and functions properly. It will work fine several times and then it will turn on, the fan will run, but it won't ignite. Just blows cold air. We've replaced the sail switch, the circuit board and the temp sensor. It still does the same thing after replacing these parts. I have no clue where to look next. It seems to be intermittent as it works fine a couple of times and then fails. Anyone have any ideas on what else I can check? Help is greatly appreciated.

Camper is a 2018 Laredo 325RL.

So I had a similar situation in my house. Furnace would light the second time or sometimes not at all. Very intermittent. I fooled with it one day, called the furnace guy the next day, and it worked perfect for him.

One day later it went out for good. Would try to light and not light but the system thought it had so it would just run and blow cold air.

Turned out to be a bad gas valve. Replaced it and it worked perfect ever since. Now I’m not sure if these furnaces have such a thing to replace. But worth a look!

[Ram Nation]

It sure does have a gas valve. That's what happened on our Alpine. I ordered a sail switch extra board and valve plus a igniter just for spare parts, turned out to be my gas valve.

[Gordan D]

So is replacing the gas valve a DIY kind of thing?

[chuckster57]

Originally Posted by Gordan D

So is replacing the gas valve a DIY kind of thing?

Yes and no. You’ll have to remove the furnace and take it apart. I would verify that’s the issue before changing it.

You can take the furnace out and “bench test” it. PM if you’d like the process.

[jasin1]

Have to be careful with diagnosing furnaces or any appliance for that matter..
I’m not saying it couldn’t be a gas valve but let’s just say it’s a loose ground wire or ill fitting molex connector plug or female spade connector that looks like it’s on but is really pushed down between the plastic and the outside of the female connector…

You order a gas valve or sail switch and you remove everything,disconnect wires and you change the gas valve…you put everything back to gather but this time you tighten the ground completely or you push the spade connector on properly…

Voila! It works now! …see it was the gas valve!…nope you just fixed the real issue in the process

We used to be able to do even exchanges on in warranty hvac parts for years and years ..they just swapped out the part no questions asked when it was still in warranty.
Not anymore

Carrier Corp makes us pay for the new warranty part…they ship the questionable part back and test it…if it’s bad you get the credit..if not you payed for it

Too many “parts changers” ruined it for everyone…guys that didn’t know how to troubleshoot would just order “all” the parts they thought could be a problem because warranty covered it

Have someone test the gas valve

You would check for proper voltage at the gas valve itself and use a manometer to see if you have gas on both sides of the valve when 12 volt is present ( tstat is calling for heat)
..on residential furnaces you can have bad igniters , sticking temp limits, dirty flame sensors, stuck pressure switches…many many things

I will add that In my 35 years of hvac it’s almost never the gas valve. They are built pretty foolproof and robust. At least for residential furnaces..it does happen but not often. Usually a weaker link in the chain

[ChuckS]

Don’t know which furnace you have… Dometic Atwood or Suburban..

You’ve changed parts.. when it won’t light off now after running a few times but blower comes on have you checked outside and listened :
1. Sound of igniter firing
2. Smell of propane

Since blower motor is spooling up I’d have to test that sail switch again and see if there is continuity across it

I’d also double check the connections to the circuit board..

Lastly if you don’t hear the igniter firing and smell a whiff of propane I would have to pull the combustion chamber out and verify it’s not all rusted up and check the ignitor itself for condition and proper gap setting

If you have the skill sets you can TS fairly easily and the service manuals are available on line to help you

[jsb5717]

Agree....diagnosing can be challenging. It's possible that just jiggling all of the wires and connectors to make sure they have good contact on the furnace main board is a good idea. That fixed 3 previous furnaces for me. I think that's less likely with the newer furnaces, though, with their better spade connections. However...worth a shot.

As mentioned, it could be gas flow but perhaps it's the propane regulator, not the gas valve. Furnaces have a very high demand for proper flow. When the furnace fails, is there any other gas appliance running that isn't running when the furnace is working? All of the other gas appliances can work just fine with less gas flow, but not the furnace. If the regulator is border-line faulty then perhaps adding another appliance drops the flow just enough for it to fail.

I had a problem with our 2018 furnace that was solved with a new propane regulator so I'm just thinking out loud with the OP's furnace. But for the sake of troubleshooting thought it was worth mentioning.

[jasin1]

Originally Posted by jsb5717

Agree....diagnosing can be challenging. It's possible that just jiggling all of the wires and connectors to make sure they have good contact on the furnace main board is a good idea. That fixed 3 previous furnaces for me. I think that's less likely with the newer furnaces, though, with their better spade connections. However...worth a shot.

As mentioned, it could be gas flow but perhaps it's the propane regulator, not the gas valve. Furnaces have a very high demand for proper flow. When the furnace fails, is there any other gas appliance running that isn't running when the furnace is working? All of the other gas appliances can work just fine with less gas flow, but not the furnace. If the regulator is border-line faulty then perhaps adding another appliance drops the flow just enough for it to fail.


I had a problem with our 2018 furnace that was solved with a new propane regulator so I'm just thinking out loud with the OP's furnace. But for the sake of troubleshooting thought it was worth mentioning.

Good thought…I will say I don’t work on rv furnaces ..I think chuckS and a few others are more experienced..

To your point …there was a post a while back where a propane fridge would go off when the stove was lit or vice versa. Someone else also had a kinked line when the slide was opened or closed so you might be on to something…that’s why I always check with a manometer for everything lp related …I usually clock a gas meter for natural gas

[Ram Nation]

My problem just happened to be the gas valve which I had ordered along with other parts to have in case I needed them down the line. It sounds to me like you know how to read voltages with a multimeter. There are plenty of articles on how to troubleshoot furnaces. I think you already have a pretty good grasp of what is supposed to happen, just take your time and follow the steps one by one, you'll figure it out. It isn't brain surgery.

[jasin1]

Originally Posted by Ram Nation

My problem just happened to be the gas valve which I had ordered along with other parts to have in case I needed them down the line. It sounds to me like you know how to read voltages with a multimeter. There are plenty of articles on how to troubleshoot furnaces. I think you already have a pretty good grasp of what is supposed to happen, just take your time and follow the steps one by one, you'll figure it out. It isn't brain surgery.

Hope you didn’t take it that I thought you were wrong…just saying it can get expensive throwin parts at it

[ChuckS]

Easy enough once you have access to the control board to verify 12 volts is being sent from the control board to the solenoid .. if good then you could also verify the furnace LP solenoid is opening when it receives 12 volts

[wiredgeorge]

I would purchase a good electric space heater and fix the propane if you really need to heat the underbelly. Unless the problem is kind of simple like the regulator or such, sounds like the fixing of the heater is a bit more involved than i would care to undertake.

[CedarCreekWoody]

Originally Posted by wiredgeorge

I would purchase a good electric space heater and fix the propane if you really need to heat the underbelly. Unless the problem is kind of simple like the regulator or such, sounds like the fixing of the heater is a bit more involved than i would care to undertake.

And yet you can rebuild motorcycle carburetors blindfolded! To each their own. Lo.

[Ram Nation]

Originally Posted by jasin1

Hope you didn’t take it that I thought you were wrong…just saying it can get expensive throwin parts at it

No Sir I was referring to the OP and his ability for checking his furnace. Didn't take your comment out of context at all. Been a long time since I graduated Devry, 1981 and I know things change with electronics. I just figured he knew how to check his limit switch and sail switch so I'm sure with a good meter he could move on.

[Ram Nation]

Forgot to add, if you look at my post about the valve I WAS not telling the OP what I thought to do. I was merely saying that rv furnaces have a gas valve. Funny how people take things out of context. Seems like that's common on these type forums. I guess from now on I'll stay out of the way and let the experts tell it.

[chuckster57]

Originally Posted by ChuckS

Easy enough once you have access to the control board to verify 12 volts is being sent from the control board to the solenoid .. if good then you could also verify the furnace LP solenoid is opening when it receives 12 volts

And almost that easy if you have to take the furnace out.

[jasin1]

Originally Posted by Ram Nation

Forgot to add, if you look at my post about the valve I WAS not telling the OP what I thought to do. I was merely saying that rv furnaces have a gas valve. Funny how people take things out of context. Seems like that's common on these type forums. I guess from now on I'll stay out of the way and let the experts tell it.

No need to stay out of the conversation…that’s what makes the forum’s interesting…you never know what bit of info may solve a problem

I’m also not an expert on rv systems ….when I started on the forum I thought everything from my residential knowledge would transfer over to rv’s ….I was wrong…the guys on here that have lived with and worked on theses systems know all the little nuances and fixes

Keep contributing

[08quadram]

I follow this channel on YouTube. This video he goes into great detail on troubleshooting a furnace.
https://youtu.be/fGunURT1UMY

If you own an rv, he is worth watching.

[Ram Nation]

Originally Posted by 08quadram

I follow this channel on YouTube. This video he goes into great detail on troubleshooting a furnace.
https://youtu.be/fGunURT1UMY

If you own an rv, he is worth watching.

Yes Sir, pretty much sums it up nowadays. If you can listen and see, Youtube pretty much explains all.