As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FIRE WARNING LIGHT CAME ON. PULLED FIRE HANDLE AND DISCHARGED FIRE BOTTLE, LIGHT WENT OUT. HAPPENED WHILE IN CLIMB 10 MINUTES AFTER TAKEOFF AND 20 MINUTES AFTER APU SHUTDOWN ON GROUND. APU FIRE DETECTION TEST OK AFTER SHUTDOWN. *S/D* FOUND B-LOOP UPPER SENSING ELEMENT WITH CHAFING AT SECOND CLAMP FROM LEFT CONNECTOR. REPLACED UPPER AND LOWER FIRE LOOPS, OPS CHECKED OK.