As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKE OFF WITH APU OFF. RECEIVED AN OVERHEAT DETECTOR AND WITH APU DETECTOR INOPERATIVE LIGHT. RETURNED TO DEPARTURE. ACFT GROUNDED. VERIFIED FAULT. REPLACED APU TAIL PIPE OVERHEAT DETECTOR ASSY WITH SERVICEABLE ONE. ACCOMP APU FIRE DETECTION OPS TEST, TEST PASS REF MM 26-15-00-710-801 & 26-15-01-400-802.