As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR - CREW REPORTED AFT A5 LAVATORY SMOKE DETECTOR WENT OFF. NO SMOKE WAS FOUND AND FLIGHT ATTENDANT RESET. EMERGENCY DECLARED FLIGHT LANDED LHR WITHOUT INCIDENT. AT GATE ARRIVAL ALARM WENT OFF AGAIN. REPLACED SMOKE DETECTOR IN LAVATORY A5. INSPECTED WATER HEATER, HEAT STRIP IN TRASH CAN, AND FIRE EXTINGUISHER NO DEFECTS FOUND. SYSTEM GROUND CHECK NORMAL OPERATION.