Alan,
I'm not sure if you have the same furnace in yours, that we have in ours. Our '05 has the "inside-outside" exhaust-intake" on it. (The "screen" on the outside of the furnace is almost square.
Our '04 had the two separate pipes. Exhaust on top, and intake below it. The "screen" on the outside of the rig was a very pronounced rectangle.
The new furnace had the same problem, though from the first day we had temps below 40 at night. Turns out there is supposed to be a piece of packing, or a bushing, between the inside exhaust pipe, and outside intake pipe. It wasn't in the rig when we bought it.
When the dealer finally replaced the furnace, and was installing it in my rig, they noted the missing bushing, and told me about it.
It must have been just loose enough when cold that the intake was sensing exhaust gas when the furnace would light for a few seconds, and then turn off after trying a few more times.
It's a dealer thing, either way, of course. And if it's a control board, (which they replaced in mine to no avail, as soon as I had a 40 degree night,) the dealer will have to do that. And they’d have to do the bushing, of that's missing. But only if you have the same squarish "screen" on the side of your rig.
When it's solved, let us know.
Steve
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