As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: FLIGHT ATTENDANT IFE PANEL NO COOLING LIGHT WAS ON FOLLOWED BY IFE SMOKE DETECTED LIGHT. TURNED OFF IFE/PASSENGER SEATS AND CABIN/UTILITY SWITCHES AS A PRECAUTION. RETURNED TO LHR AND DELCARED EMERGENCY. TROUBLESHOOT PER FIM 21-27-00-810-858. REPLACED IFE COOLING FAN PER AMM 21-27-35.