As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JUST PRIOR TO LEVEL OFF AT FL350 APU DET INOP ILLUMINATED. APU WAS OFF AT THE TIME AND REMAINED OFF FOR THE REMAINDER OF THE FLIGHT. GROUNDED - YES. DIVERSION TIME 10 MINUTES - REMOVED AND REPLACED APU LOWER HEAT DETECTOR ASSEMBLY REF AMM 26-15-01. WHEN ACCOMPLISHING APU FIRE BITE TAIL PIPE FAULT ILLUMINATED. REMOVED AND REPLACED APU TAIL PIPE DETECTOR REF AMM 26-15-01.