As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING APU START WHILE PARKED AT GATE, APU FIRE WARNING ANNUNCIATED. APU FIRE BOTTLE WAS DISCHARGED. MAINTENANCE INSPECTED APU AND FOUND NO EVIDENCE OF FIRE. FIRE BOTTLE WAS REPLACED. SURGE VALVE DUCT SEAL WAS FOUND RUPTURED AND WAS REPLACED.