As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURNBACK / DECLARED EMERGENCY. APU FIRE WARNING BELL AND FIRE WARNING LIGHT ILLUMINATED DURING FLIGHT. DISCHARGED APU FIRE BOTTLE, LIGHT DID NOT EXTINGUISH. INSPECTED APU COMPARTMENT, NO EVIDENCE OF FIRE. DEFERRED PER MEL. LATER AT HOU REMOVED AND REPLACED APU FIRE DETECTION LOOP M515 PER MM.