You've probably got clogged jets. If the top of the burner is removable, remove it. Mine gets a white build up around the jet holes. A dry brush will flake it offf. Be sure to pull out from the burner, not in or back and forth to the keep the burner free from debris.
My area is switching over gas supplies to a lower BTU mix as the high quality sources are running out. I think the extra filler in the gas contributes to the white crud. I didn't used to get it on the old gas mix.
Phil |