As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW HAD A NR1 ENG FIRE WARNING LIGHT ON DURING TRAINING FLIGHT WITHOUT ACTUAL FIRE. CAME BACK TO THE AIRPORT. TROUBLESHOOTING REVEALED THAT FIRE DETECTOR LOCATED ABOVE COMBUSTION CHAMBER AREA WAS SENDING A CONTINUOUS FIRE ALARM SIGNAL TO THE SYS EVEN WITHOUT AN ACTUAL FIRE. PART REPLACED AND SYS TESTED SERVICEABLE. ACFT RETURNED TO SERVICE.