As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLE FLIGHT 3234 THE CREW REPORTED A APU FIRE WARNING IN FLIGHT AFTER START. THE APU WAS SHUT DOWN AND THE FIRE BOTTLE WAS EXTINGUISHED. THE AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE INSPECTED APU AND FOUND NO EVIDENCE OF FIRE OR NO DEFECTS. THE APU WAS OPERATIONALLY CHECKED AND NO DEFECTS WERE FOUND. THE FIRE BOTTLE WAS REPLACED AND THE AIRCRAFT WAS RELEASED FOR SERVICE.