As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURNBACK, APU FIRE WARNING LIGHT AND BELL WENT OFF AT APPROX 1000 FEET. COMPLIED WITH AIRCRAFT PROCEDURES CHECK LIST, AND DISCHARGED APU FIRE BOTTLE. APU FIRE WARNING LIGHT WOULD NOT EXTINGUISH. COMPLIED WITH APU COMPT AND APU INSP. NO EVIDENCE OF FIRE NOTED.