Someone else here was having a similar problem a few days ago.
Not sure if they got it corrected.
It may be that there is a blockage in the burner tube. Spider web or dirt dauber nest.
I have had dirt daubers build in the burner tube. If you are able to unscrew the burner tube from the orifice it is easy to clean.
I could not, as the tube was rusted to the orifice.
I had to use a wire going in through the slots and vent hole to clean it. Don't stick anything in the orifice, which is the tiny hole that lets gas into the burner tube.
Another option is to buy a new orifice and burner tube.
