What was found
(CAN) THE FLIGHT CREW WAS UNABLE TO PRESSURIZE THE ACFT DURING DEPARTURE. IN CONJUNCTION WITH MAINTENENCE, FLIGHT DISPATCH & FLIGHT OPERATIONS, THE ACFT WAS DIVERTED BACK. THE FLIGHT MAINTAINED 9000FT ALTITUDE, WHILE "DUMPING" APPROXIMATELY 70,000 KG OF FUEL TO LOWER THE EVENTUAL LANDING WEIGHT. THE ACFT DID LAND AT A WEIGHT OF APPROXIMATELY 263,900 KGS, WHICH IS 12,600 KG ABOVE THE MAXIMUM STRUCTURAL LANDING WEIGHT. CFR WAS CALLED OUT AS A PRECAUTION AND MAINTENENCE ALSO MET THE ACFT. THE RETURN LANDING ON RUNWAY 23 WAS OTHERWISE ROUTINE. THERE WAS NO ADVERSE PASSENGER REACTION. OVERWEIGHT LANDING INSPECTION ACCOMPLISHED IAW TASK 05-51-35-210-801 PHASE 1 DUE TO PILOT SMOTH LANDING. NO OVBIOUS DAMAGE OR LEAKS FOUND. ACFT RELEASED FOR SERVICE.