Just a quick guess- under the fridge
BTW furnaces are a collection of parts, including some safety switches. One of them could be kaput. Yours is probably a Suburban SF-42F, which fortunately came w/a 2 year warranty.
There is a normally closed limit switch in the tstat line to the control board that, if it fails open, would preclude a call from the tstat to reach the control. Likewise the module board could be bad. Or could just be a finicky female connection wants some attention and can't figure any other way to get it than withhold her services.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project