Look at this trouble shooting page. Especially down where it talks about keeping the burner tube adjusted and clean. Bugs can get in and screw up the works.
Hope this helps.
You might also have a valve shut. This happen to us on our first rv, the dealer didn't tell us about it. It took us 3 days to figure it out, it was behind a wall in the basement. Hope this helps.
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Jim & Linda with Candy Bar and Misty
'06 Chev 3500 DuraMax w/Banks
'10 Seville
'09 GL1800 Hannigan Trike
GSCM USN(Ret)
ALR,PGR,VFW 3788, AL460