"POOF" From LP Heater

[trvlngnrs]

While outside, removing the polarity monitor, I noticed the bedroom LP
heater would run for awhile then I would hear a "POOF". The heater
would run for a few minutes and "POOF" again.

I have already vacumed the areas I could get too, but really couldn't
get to very much of the heater due to the metal box it's in.

I've been told a couple times to clean it, but how? Do I need to
disconnect the gas line and take it out? Is there a way to open up the
heater box to clean inside it?

TIA,
Steve Harrie
'86 PT38