As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EAT- ON FLIGHT 2134 ENROUTE SEA TO EAT MASTER WARNING AND CHECK FIRE DETECTION ILLUMINATED. DURING EMERGENCY CHECKLIST SELECTED LOOP A ONLY BECAUSE LOOP B WAS ILLUMINATED. MASTER WARNING AND CHECK FIRE DETECTION WENT OUT. REMOVED AND REPLACED SWITCHING VALVE. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.