As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HEATER CORE RETURNED TO US BY CUSTOMER AFTER PURCHASING AN EXCHANGE/OVERHAUL HEATER. TEAR-DOWN/CLEANING OF CORE REVEALED COMBUSTION HEAD WITH A 3/16 X 1/4 INCH HOLE IN THE WALL OF THE COMBUSTION HEAD. THIS IS THE THIRD HEAD WE HAVE FOUND WITH A HOLE IN IT. A PRESSURE DECAY CHECK OF THE HEATER ASSEMBLY WILL FIND THESE HOLES QUICKLY, IF PERFORMED. RECOMMEND PRESSURE CHECK OF ALL COMBUSTION AIRCRAFT HEATERS FOR CONTINUED SAFE HEATER OPERATION.