As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT OF CLT THE CREW CEREIVED A RED GEAR DISAGREE MESSAGE AND THE GEAR DID NOT RETRACT. THIS WAS CONFIRMED BY THE TOWER. THE CREW RAN THE QRH, DECLARED AN EMERGENCY AND RETURNED TO CLT FOR MAINTENANCE. THEY LANDED SAFELY ON RUNWAY 36R AND TAXIED TO THE GATE. REMOVED AND REPLACED LANDING GEAR SELECTOR VALVE IAW CRJ 900 AMM 32-32-10-000/400-801. OPS CHECK GEAR EXT / RETRACTION SYS GOOD. SELECTOR VALVE LEAK CHECK GOOD.