Furnace Won’t Light

[ZAdventures]

Wondering if anyone else has had this issue…since we bought our Imagine our furnace is a bear to get lit. It is very sporadic and has never been consistent. It will cycle thru several times and then finally light…then the next time it calls for heat it will light after the second try….then the next time it will take 20 tries to light if it does at all and so on.

As luck would have it our slide out failed on our first trip out so while it was at the dealer getting that fixed we told them about the furnace not lighting and to check it out and were told they ran it all day with no issues. Said they made some regulatory adjustments, but the rest of the system seemed fine.

Next trip out…same thing…light immediately, then took a dozen cycles.

Anyone else have this issue and find cause? Wondering if it’s a bad regulator?

Any thoughts are appreciated!

[Cate&Rob]

My initial thought would be a sticky sail switch. This is the device that the fan blows closed to tell the circuit board that it is OK to light the burner.

Rob

[ZAdventures]

Hmm…might be since everything else works fine. We had that issue on a tent trailer, but haven’t checked that out on this one yet. We’ll have to check it out!

Cute puppies! Thought the one on the left was a sheltie at first…our Zoey is a sheltie 😁

[Cate&Rob]

ZAdventures

Dogs are 40 lb littermate sisters. Mother was a Border Collie. Father was a Rough Collie. Molly is often thought to be a “big” Sheltie. Angel definitely looks like her Border Collie mother.

Rob

[TedS]

Check the igniter gap.

[ZAdventures]

We’ll check that out too Ted…thanks!

[howson]

ZAdventures -- doubt it's the sail switch. It could be...but unlikely the sail switch would suddenly be intermittent when the furnace attempts to light. The furnace would not attempt to light if the switch was a problem.

Based on the sequence of operation, I suspect there's an electrode-related issue, too. (Could be the main board, wiring to the main board, flame sensor positioning or the flame sensor itself). Below is the generic sequence of operation for a Suburban furnace (from their Service Manual).

Note that (unfortunately) the furnace is a component that to troubleshoot usually requires removal from the RV. The vast majority of installations are impossible to troubleshoot with it installed in the camper.

[ZAdventures]

Didn’t think it was the sail switch…when it went back to the dealer they were unable to replicate the issue. Said it started fine every single time it tried to light during the time it took them to repair the failed slide. We recently went camping at 8600 feet and thought perhaps it’s an altitude problem and the regulator needed adjusting. Trying to adjust the regulator for an extended amount of time it ignited, but once the heater turned off and tried to ignite again it would just cycle. We’ve tried the furnace at a few different elevations, but haven’t had it consistently light as the dealer said they did. We’re trying to figure out if it’s an easy fix like a new regulator or if it needs to go back to the dealer, which is a 5 hour drive away…

[Jlawles2]

Are you using a gauge to check the pressure of the regulator? It could be possible that you are using too much pressure and the flame cannot light due to high altitude lack of oxygen. I have hear of but not seen personally over pressure causing a system to not light (unless you count my propane torch).

Remember the gas pressure of a propane system is measured in INCHES of WATER not PSI. 11 inH2O is less than 0.5 psi.