As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED DUCT MON WARNING VALVES CLOSED, AC WOULD NOT MAINTAIN PRESSURAZATION. CREW ELECTED TO RETRUN TO DEPARTURE AND LANDED WITHOUT INCIDENT. MAINT REMOVED AND REPLACED THE ANTI-ICE AND LEAK DETECTION UNIT. NO OTHER DEFECTS NOTED AND ACFT WAS RELEASED FOR SERVICE. (K)