it's late so you have likely figured it out by now....hope so....
but if not
it might be insects or something in the burner. Seems like it doesn't take much of a spider to mess it up. I had something in mine once and I never saw it....someplace either in the area right where the burner is, or in the chimney (?) tube, or the gas jet. I blew it all out with an air compressor and it worked fine after.
I'd take the cover off outside, flip on the LP switch then run around outside to watch what is happening...
is it trying to light?
is it sparking?
__________________
|