As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING INITIAL CLIMB CREW RAN THE CLIMB CHECKLIST, AT THIS TIME FOUND THE A/C WAS NOT PRESSURIZING. RAN FUEL NUMBERS AND DETERMINED THEY WOULD BE VERY CLOSE TO MIN FUEL WITH THE FUEL ON BOARD, DIVERTED BACK TO LIT WITHOUT FURTHER ISSUE. EVALUATED & DEFERRED PER MX CONTROL IAW MEL 21-30-5-1 CAT A ID# 45713. LATER PERFORMED OPS CHECK OF PRESSURIZATION SYSTEM IAW Q400 MM 21-31-00-946-002, OPS CHECKED GOOD.