As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT 1631 - AFTER TAKEOFF, AIRCRAFT WOULD NOT PRESSURIZE IN AUTO, STANDBY, OR MANUAL. NO DOOR WARNING LIGHTS WERE ILLUMINATED. FLIGHT RETURNED TO FIELD AT PIT AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE PRESSURIZED AIRCRAFT TO 4 PSI AND CHECKED OUTFLOW VALVE IN AUTO AND MANUAL. OPS CHECKED GOOD. CHECKED ALL DOORS FOR LEAKS AND OPERATION. DOORS CHECKED GOOD. AIRCRAFT OK FOR SERVICE. (X)