As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WOULD NOT PRESSURE AFTER TAKEOFF WITH TWO PACKS ON AND OUTFLOW VALVE CLOSED. COMPLETED UNSCHEDULED CABIN PRESSURE CHANGE CHECK LIST WITH NEGATIVE RESULTS. PERFORMED PRESSURIZATION TEST PER MAINTENANCE MANUAL 21-30-0 PAGE 501 TO 503. FOUND LEFT OUTFLOW VALVE STAYING OPEN. REMOVED AND REPLACED LEFT OUTFLOW VALVE, OPERATIONAL CHECK GOOD.