What was found
DEN - AIR TURNBACK -C - WHILE EN ROUTE ACFT RECEIVED ECAM MESSAGE FOR VENT SKIN FAULT. DURING TURN AT DEN DEACTIVATION OF THE VENT SKIN AIR VALVE WAS ACCOMPLISHED. UPON TAKEOFF FROM DEN TO LAS ECAM MESSAGE REAPPEARED AND ACFT WOULD NOT PRESSURIZE, ACFT TURNED BACK TO DEN AND MADE UNEVENTFUL LANDING. MX TROUBLESHOT SYSTEM & FOUND VENT SKIN AIR VALVE IN OPEN POSITION. DEACTIVATION OF VENT AIR SKIN VALVE IN CLOSED POSITION WAS CORRECTLY RE-ACCOMPLISHED AND CPC TEST 1 AND 2 WAS PERFORMED WITH NO DEFECTS NOTED, ACFT WAS RETURNED TO SERVICE. REPLACED THE VENT SKIN AIR VALVE. NO FURTHER DISCREPANCIES HAVE BEEN REPORTED.