As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CRUISE FLIGHT, NOXIOUS FUMES FILLED CABIN. CREW SUSPECTED HEATER AND TURNED OFF HEATER SWITCH. FUMES DISSIPATED. TURNED HEATER BACK ON AND FUMES RETURNED. RETURNED FOR UNEVENTFUL LANDING. MAINTENANCE INSPECTED HEATER AND FOUND COMBUSTION BLOWER INOPERATIVE. REMOVED AND REPLACED COMBUSTION BLOWER ASSEMBLY.