What was found
(CAN) ACARS MESSAGE THAT THEY HAD SMOKE/FUMES IN THE FLIGHT DECK, FOLLOWED BY ENGINE ADPT HEAT 1 CAUTION LIGHT ILLUMINATED. CAPTAIN ADVISED SOCC OF SITUATION, AN EMERGENCY WAS DECLARED AND ACFT WAS TURNED BACK. ADVISED DUTY OFFICER AND MOC OF EVENTS. MOC ADVISED TO SHUTDOWN ACFT NORMALLY, THE 24-HR SYSTEM CHECKS WERE NOT C/O. MAINTENANCE INVESTIGATED SITUATION AND CONFIRMED INTAKE HEATER UNSERVISEABLE. MAINTENANCE REPLACED INTAKE HEATER AND UPLIFTED OXYGEN BACK TO SPEC. ACFT RETURNED TO SERVICE.