What was found
AT 25000 FT, DURING CRUISE, THE FIRE BELL CAME ON . NO OTHER FIRE INDICATIONS VISIBLE. ALL ENGINE INDICATIONS WERE NORMAL, EXCEPT THE NR 2 FUEL TEMP SHOWED +99 DEGREES,. IAW THE ABNORMAL FUEL TEMP CHECK LIST, TURNED ON THE NR 2 FUEL BOOST PUMP, NR 2 FUEL TEMP CAME BACK DOWN TO THE NORMAL RANGE. WOULD CLIMB BACK TO 71 DEGREES SHORTLY AFTER TURNING THE NR 2 BOOST PUMP OFF. AIRCRAFT REMOVED FROM SERVICE. REMOVED AND REPLACED THE NR 2 ENGINE FUEL HEATER THERMAL ACTUATOR IAW AMM 73-11-05-000/400-801. LEAK CHECKED GOOD. AIRCRAFT RETURNED TO SERVICE.