As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER THE CREW TURNED ON THE HEATER, IT OPERATED NORMALLY FOR A FEW MINUTES UNTIL SMOKE WAS OBSERVED COMING FROM THE COMBUSTION AIR INTAKE. INVESTIGATION REVEALED THE COMBUSTION AIR PRESSURE SWITCH STUCK CLOSED AND THE COMBUSTION BLOWER FAILED SUBSEQUENTLY CAUSING A HEATER FIRE OUT OF THE COMBUSTION BLOWER INTAKE.