As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - CREW RETURNED TO FIELD WHEN DURING CLIMB THEY WERE UNABLE TO PRESSURIZE THE AIRCRAFT. MAINTENANCE INSPECTED THE AIRCRAFT AND PERFORMED AN OPERATIONAL CHECK OF THE PRESSURIZATION SYSTEM. OPERATIONAL CHECKS WERE GOOD. NO DEFECTS WERE NOTED AND THE AIRCRAFT WAS RETURNED TO SERVICE.