Furnace kicks on, but then goes off within a few seconds ??

[Bierp]

+1 for checking the LED code. If it's the insufficient pressure code, that's likely the sail switch. I guess it's pretty common and often just requires a cleaning rather than a replacement.

I went through this last month.

In the past I've had water on the board (in SOB) and that was more of a nuisance, but it was easily removed and dried.

LED code will get you checking the right thing, including gas feed if that's actually the issue.

Good luck!