As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE PILOT REPORTED DETECTED A BURNING RUBBER ODOR IN THE CABIN WHEN THE HEATER WAS TURNED ON. THE MECHANIC INSPECTED THE HEATER TUBES, VENTS, AND THE BLEED AIR SYS WITH NO DEFECTS NOTED. REMOVED HEATER CONTROL COVERS AND FOUND THAT A PIECE OF THE BLOOD BARRIER HAD CRACKED OFF AND WAS ON THE HEATER VALVE. SHOWED SIGNS OF SCORCHING. NO OTHER SIGNS OR DAMAGE FOUND. THE ACFT WAS THEN RETURNED TO SERVICE.