As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, FIRE WARN MASTER LIGHT ON GLARESHIELD CAME ON. AIR TURNBACK. CK WIRE FROM FIRE DET CNTRL UNIT M819 PIN 14 OF D1478 FOR A GROUND. WIRE CK GOOD WITH FLUKE. SUSP FIRE DET CNTRL UNIT TO BE THE PROBLEM. REMOVED AND REPLACED ENG FIRE DETECTION UNIT PER EA 1-2610-56855 OPS CK GOOD. FOUND LEAK ON INLET SIDE OF FUEL HEAT AIR VALVE. REPLACED GASKETS PER B727 MM 73-14-011. OPS CK GOOD.