95 fleetwood

I think the hardest part of my furnace rebuilds was figuring out where all the screws are hidden! My two furnaces are next to each other on a shelf in one of the basement compartment on the street side.
The first obstacle was a face plate across the front of the furnaces. Three of the screws across the top of the plate where hidden behind the basement seal. I had to partially remove the seal to get to the screws.
A couple screws holding the furnaces in place, disconnect gas & electrical & the furnaces slid out. Note the forward furnace was a size larger than the rear furnace so note what furnace goes where if your working with dual furnaces.
I have the complete job documented on my web site. I believe most of the older posts have lost some PICS from then the site when I had to do a backup/restore.
It's nice to get into those furnaces and give them a god cleaning. I found some critter nests behind one of the furnaces!

NO l haven,t torn it down, not really sure how but willing to give it a try, is it very hard,

I have torn down both my hydro flame furnaces. Have you cleaned the control board and contacts?

Sail switch is toward the rear on the left side. Blow out the compartment good with compressed air.

it,s a 95 fleetwood prowler, 35 ft. with a Atwood hydro flame furnace. model 8500

Could be bedris blocking the air flow from activating the sail switch.
What is make and model of your furnace?

Low voltage is the #1 cause of this-- fan speed not enough to close the sail switch.

What is voltage at the furnace?

Obstructed air return and/or closed vents and/or crushed ducts can also restrict air flow enough to cause the sail switch to stay open.

Gas valve and ignitor ONLY work once the PC board sees the closed sail switch.