What was found
(CAN) ENGINE HIGH STAGE EICAS MESSAGE CAUSED FLIGHT CREW COMPLETE QRH CHECKLIST AND SELECT NR 1 ENGINE BLEED TO OFF. APPROXIMATELY ONE HOUR LATER, CREW NOTICED CABIN ALTITUDE AT 10,000 FEET RISING SLOWLY. DESCENT INITIATED AND NORMAL PRESSURIZATION RECOVERED AT APPROXIMATELY FL 270. POST-FLIGHT INVESTIGATION REVEALED A FAULT WITH THE NR 1 ENGINE HIGH STAGE PILOT VALVE. THE VALVE WAS REPLACED.