As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT, THE CREW WAS UNABLE TO PRESSURIZE THE AIRCRAFT. THE CREW CALLED MAINTENANCE CONTROL WHO INSTRUCTED THEM TO RETURN TO DCA. MAINTENANCE INSPECTED AND REPLACED THE FORWARD OUTFLOW VALVE IN ACCORDANCE WITH DORNIER MAINTENANCE MANUAL 21-00-00. OPERATIONAL CHECKS WERE PERFORMED AND THE AIRCRAFT WAS RELEASED FOR SERVICE.