What was found
AIRCRAFT WAS NOT GROUNDED: 3 HOURS 20 MIN INTO FLIGHT, LEVEL CRUISE ALT. 30,000FT. ECAM BRAKES HOT. ON WHEEL PAGE BRAKE 3 TEMP BETWEEN 350? ? 550? ALL OTHER TEMPS 20?. DESCENDED TO 18,000 FT. SLOWED TO 210 KNOTS PERFORMED ECAM PROCEDURE. TEMP ON BRAKE 3 IMMEDIATELY RETURNED TO 20? UPON GEAR EXTENSION. RETRACTED GEAR, CLIMBED, CONTINUED FLIGHT WITH ALL NORMAL INDICATIONS. MAINTENANCE REPLACED THE #3 BRAKE TEMPERATURE SENSOR AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 32-47-15.