What was found
(CAN) DURING A TAKEOFF A SMELL WAS NOTED AND INCREASE DRAMATICALLY DURING THE CLIMB. CREW NOTED THAT THERE WAS NO VISIBLE SIGN OF SMOKE. CREW RETURNED TO BASE FOR INVESTIGATION. MAINTENANCE CARRIED OUT AN APU START, BLEED ON, SMELL PRESENT FOR 2 MIN. THEN DISAPPEARED. ENGINE RUN PERFORMED NO SMELL. DC CONTACTOR BOXES CHECKED, NO FAULT. AREA AROUND WATER BOILER INSPECTED, NO FAULT. EPCU CHECKED FOR FAULT CODES, NO FAULT. CDS CHECKED, NO FAULT. ENGINE RUN PERFORMED AGAIN, NO FAULT. AIRCRAFT RETURNED TO SERVICE.