As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH TO MOB - WHILE CLIMBING THROUGH 1,500 FEET, CREW RECEIVED RIGHT PACK HIGH PRESSURE CAUTION MESSAGE ACCOMPANIED BY FAULT LIGHT INDICATION ON RIGHT PACK BUTTON. CREW FOLLOWED QRH AND MESSAGE REMAINED. THE PACK WOULD NOT RECYCLE AND THE AIRCRAFT WOULD NOT PRESSURIZE DUE TO THE LEFT PACK BEING ON MEL. THE FLIGHT THEN RETURNED TO IAH AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE PACKS AND FOUND THE DUAL PRESSURE REGULATOR VALVE ON PACK 2 WAS STUCK OPEN. AFTER REPLACING THE DUAL PRESSURE REGULATOR VALVE THE RIGHT PACK OPERATED NORMALLY.