Atwood Furnace Lockout

I doubt whether it is the high temperature limit switch.
You do not have to get to it to test it. you should be able to test it via the wires. the blue wire from the circuit board goes to one side of limit switch. There should be a white wire off the other contact. Use an Ohm meter to check for continuity.
Since the unit tries to light and goes into lock out means it is getting power through the sail switch and limit switch.
Have you checked continuity on the gas valves two coils? Should separate the wiring to verify each coil separately. Have you checked the gas valve ground? Have you cleaned the circuit board connector?

Not sail switch, but limit switch.

If you are talking getting to the sail switch, you normally would not. Get a can of compressed air. Use the straw that comes with it. Sail switch is on top of the blower assembly to the rear on the right.
Doubt that is problem.

Ok,yes the furnace tries to light three times(three clicks) before indicating lockout mode.I checked voltage at board on limit switch(white wire) and had 12v. Not sure what voltage is on other side of limit switch.Still trying to figure out what all I have to remove to get to the limit switch and the difficulty factor. Won't be able to get to it until this weekend.

Ok just to clarify is it throwing a code for ignition lockout? If so make sure the unit & gas are CUT OFF. Tooth brush & very light carb cleaner to clean the ignitor. Make sure to wipe off all the carb cleaner AND let it evaporate till dry. Very flameable stuff (as you probably know) so again make sure all is turned off.

gb76087 wrote:
Evidently I was not clear. Moved the motorhome to new location, not the furnace.
The furnace will eventually try and start, but will not light,I.e., "igntion lockout".

OK, does the ignition system click when attempting to light? Ignition Lockout only happens AFTER it tries to light 3 times. IF the Hi temp switch is sticking, it will attempt to light and go into Ignition Lockout. You need to check for 12 volts on each wire coming from the Hi Temp limit switch. You MUST have 12 volts thru that switch for the Ignition sequence to work. I have never had to replace a Furnace board due to Lightning or voltage surge problems. Doug

gb76087 wrote:
Evidently I was not clear. Moved the motorhome to new location, not the furnace.
The furnace will eventually try and start, but will not light,I.e., "igntion lockout".

I see said the blind man.

As enblethen recommended check the igniter and burner. Furnace works just like the water heater if it doesn't ignite after a few tries it goes into a lock out. Unfortunately they don't include a switch to reset.

Also try AtWood Service Manual for additional info.

Clean your ignitor/flame sensor. Make sure it is adjusted properly.

Evidently I was not clear. Moved the motorhome to new location, not the furnace.
The furnace will eventually try and start, but will not light,I.e., "igntion lockout".

Sounds like a heat exchanger over temp. With the new location were you able to use the same amount of ducting to the coach living area? The fault should clear after the sensor cools down but if not find the 12VDC fuse that powers the furnace for controller reset.