What was found
(CAN) DURING CLIMB OUT NR 3 ENGINE FIRE INDICATION APPEARED, AFTER FOLLOWING CHECKLIST PROCEDURE NR 3 ENGINE WAS SHUT DOWN AND AIRCRAFT RETURNED TO EWR AIRPORT. FIRE INDICATION WENT AWAY AS THROTTLE WAS RETARDED TO IDLE AS PART OF ENGINE SHUT-DOWN PROCEDURE. MAINTENANCE TROUBLESHOOTING FOUND A RUPTURED FUEL HEATER PNEUMATIC DUCT. DUCT HAS BEEN REPLACED FOR RECTIFICATION OF THE SNAG AND AIRCRAFT HAS BEEN RETURNED TO SERVICE.