As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT NR 6296 - IAD-RON - DURING CLIMB, AN UNSCHEDULED LANDING DUE TO MANUAL PRESSURE WOULD NOT WORK. AIRCRAFT LANDED AT IAD AND RETURNED TO GATE NO FURTHER INCIDENTS. MAINTENANCE FOUND OUTFLOW VALVE SECURED OPEN. MAINTENANCE REMOVED SECURING DEVICE, OPS CHECK OK. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (M)