2006 3400RL Atwood 8535 Furnace quit working

[Desert RVer]

I've done a search on MOC for this kind of problem and there are a few closed threads but I'd like to try one more time to get some help. RV has not been used for a few months. Tested the furnace about a week ago and it would fire and flame three times and quit. Took outside cover off but didn't see anything obvious and the connections look good. Tried starting it several times and all of a sudden it started working right. Ran it for several minutes and all seemed ok. Then let it set in cool rainy weather and tried it again and today it won't start again even after several tries and even waiting between tries. Turn the furnace on, fan starts, a few seconds later can hear the gas valve open, flame starts for a few seconds and shuts off. Does this three times and then finally the fan shuts off. I've repeated this sequence several times today. Get the "ignition lockout fault" three blinks of the Led. Gas water heater and three burner gas stove work fine.
I've disconnected all connections and reconnected them several times in hopes to clean off any corrosion on the contacts. They do not look corroded at all. I've run a small but long wire brush in the exhaust port in case there might be any spider webs or anything in the exhaust pipe. Wire brush comes out clean with no noticeable obstructions. I'm stuck. Is the next step getting my control board checked?

[dieselguy]

It's a long shot, but try disconnecting the gas line and blowing it out from the regulator hose on back. Hold a clean rag over the exit end and see if anything comes out as in oil or debris. I know you said all other gas appliances work ... I'm just wondering about the furnace run itself.

[DQDick]

Before you even do that check the orifice and see if there is a web or bug in there. That tends to be the place they like more frequently than the exhaust.

[Desert RVer]

Thanks for the suggestions folks. Stewed over this problem for awhile and began to wonder if it had anything to do with the wet cool weather we have had recently. Took a hair dryer to the furnace control module and in about 15 minutes of drying all of a sudden the furnace started working. Now running the RV at a higher temperature to have the furnace run more often which may dry things out. But ordered a Dinosaur replacement control module ... "Fan 50 Plus pins" just in case this problem shows up again.

[Ozz]

Good troubleshooting Desert RVer! The old cause and effect method is hard to beat.
The boards are tricky, it sounded like a dirty flame rod, and I bet it was in that circuit on the board. 90% of my calls in the winter are a dirty flame rod. They are just a stainless rod placed in the path of the flame, when the flame hits the rod, it 'proves' a ground, and the gas valve stays open. It doesn't take much to insulate the rod and stop conduction.

[DQDick]

Thanks Ozz. Once again learned something from you.