Furnace Won’t Ignite: Blower Runs, Then Shuts Off in Coachman Chaparral

[Stephen_6947266ca77c6]

I have a 2019 Coachman Chaparral 27rks 5th wheel. Furnace was working great then decided to not. Currently when trying to turn it on the blower will run for about 20 seconds then **** off without the burning ever fitting up. Any ideas what I may be looking at, igniter maybe??

Thank you all!

 

[Gary RV_Wizard]

If the burner fails to light within 15-20 seconds, the furnace control board shuts off the gas valve to avoid flooding with unburned propane (which could explode). Failure to ignite could be a faulty igniter but is far more likely to be a poor mixture of air & fuel. Despite popular belief, propane will ignite only with a rather narrow range of air/fuel mix, and that mix can be disrupted by something as trivial as a spider web, insect nest, or rust flakes in the air intake or exhaust.

Listen for the snap-snap-snap sound of the igniter after the fan comes on. If you hear it, it is 99% sure the igniter is working ok.

Some years ago I wrote an article on Furnace Troubleshooting and placed it in this site's Resource library. It's still applicable to both Atwood/Dometic and Suburban RV furnaces.

 

[Kirk]

Based upon the symptoms that you described, the most likely cause is either a bad ignition probe or the sail switch not closing. If you are not on shore power the battery discharging causes lower 12V supply and that will cause the blower to turn slower, and not close the sail switch, so check your voltage.

 

[John From Detroit]

I'm going with the sail switch or air flow (Slow blower, blocked vents or ducts)
If it was the ignition probe the burner would light, shut off relight, shut off and once more than lockout. (Been there, fixed that). But since it is not lighting, sail switch

Dirty may cause it to "Stick" in the "Safe" position
Failed, it never closes
or the blow hard (Fan/blower) not moving enough air to close it

A few other things (Wire/connection failure) but far less likely, also the sail switch leads

Two more low odds things. Failed gas valve and failed control board.

OH and no propane.

 

[richclover]

I have a 2019 Coachman Chaparral 27rks 5th wheel. Furnace was working great then decided to not. Currently when trying to turn it on the blower will run for about 20 seconds then **** off without the burning ever fitting up. Any ideas what I may be looking at, igniter maybe??

Thank you all!

Welcome to the forum.
My bet: Sail switch in your furnace. Since DIY repair is above my pay grade, I hired a mobile RV repair guy to climb into the basement of my Chaparral 5’r to replace it. January a few years back, snowbird in chilly southern NV.

 

[Ohiosnowbird]

We had a similar problem. It turned out to be the sail switch. That thread is here:

Furnace troubles - it could have been worse

Honey is there anything we should be doing to maintain the furnace? Filters? Air intake? Vent cleaning? Why no, not that I know about. Blower starts. Propane lights. Nice and toasty. Blower starts. Propane lights. Nice and toasty. Blower starts. Propane lights. Nice and toasty. Blower...

www.rvforum.net

 

[Gary RV_Wizard]

Agree with the others IF the igniter isn't sparking at all. But the OP was vague about that - just says the burner didn't light. Don't go chasing the sail switch until you know whether there was any attempt to ignite the burner.

 

[John From Detroit]

I do admit I"ve seen furnaces and water heaters where the spark gap was like 3/4 inch (Way too big)
I think that was the problem with my water heater when it failed to light

Furnace was an oil burner in a house.

Gap reset worked.

 

[BBintheMountains]

I have a 2019 Coachman Chaparral 27rks 5th wheel. Furnace was working great then decided to not. Currently when trying to turn it on the blower will run for about 20 seconds then **** off without the burning ever fitting up. Any ideas what I may be looking at, igniter maybe??

Thank you all!

Sounds like sail switch. My 07 Bounder 35e did a similar process. The short period of blower running was a result of a nonfunctional sail switch.
Easy fix

 

[BBintheMountains]

You may want to feed detailed symptoms into ChatGTP
You be surprised how intuitive it can be.