Mine did something similar, I had to remove the burner tube and vacuum out several hundred asian beetles, and take the burner tube to a wire wheel as the holes were encrusted with rust, also used a metal pick to get some really bad areas. I found a new burner tube online but mine cleaned up nicely and works well now.
I seem to remember taking one of ours apart years ago and discovering that the orifice feeding the burner was partially blocked. I removed the orifice and used a fine wire to push out the particle.
Propane heater
Linear Mode
