As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT# 1621, LHR-BOS. (ETOPS) 'ENG 2 FIRE LOOP B FAULT (ENGINE FIRE DETECTION SYSTEM 2) LOOP B). REMOVED AND REPLACED ENG #2 CORE AGB LOOP B IAW AMM 26-12-17. REF LOGPAGE 4352300 ITEM #1 BY JB MX. OPS TEST OK. ETOPS GROUND VERIFICATION PERFORMED AMM 26-12-00-710-002A. BITE TEST OK. NO FAULT FOUND. FAULT HAS NOT RETURNED.