As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE NOSE DOOR OPEN WARNING ILLUMINATED AND SOUNDED AFTER GEAR RETRACTION. THE FLIGHT RETURNED TO SDF. THE AIRCRAFT WAS FERRIED TO PHL WHERE MAINTENANCE REMOVED & REPLACED THE NLG DOOR SELECTOR VALVE IAW CRJ200 AMM 32-22-20-000-801 AND 32-22-20-400-801. LEAK AND OPERATIONAL CHECKS WERE GOOD. THE AIRCRAFT WAS THEN RELEASED FOR SERVICE.