As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF AIRCRAFT WOULD NOT PRESSURIZE. BOTH AIRCRAFT PACKS DID NOT WORK AND AFTER RESETTING BOTH PACKS TO (ON) AIRCRAFT WILL NOT PRESSURIZE. RETURNED TO AIRPORT WITHOUT INCIDENT. TROUBLESHOT AIRCRAFT PRESSURE SYSTEM, FOUND CRACKED PRIMARY HEAT EXCHANGER REMOVED AND REPLACED. AIRCRAFT RETURNED TO SERVICE.