As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, CREW EXPERIENCED APU FIRE WARNING AND THE APU WAS OFF. FIRE BOTTLE WAS ACTIVATED AND THE FIRE WARNING LIGHT REMAINED ILLUMINATED. AIRCRAFT RETURNED TO HOU AND MADE AN UNEVENTFUL LANDING. INSPECTED AND NOTED NO EVIDENCE OF FIRE OR OVERHEAT CONDITION. REPLACED APU FIRE DETECTION LOOP M717 AND FIRE BOTTLE PER BOEING M/M.