As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN SELECTING GEAR UP, RECEIVED NOSE DOOR OPEN AND GEAR DISAGREE WARNING MESSAGES. RECYCLED GEAR PER QRH AND GEAR CAME DOWN NORMALLY. DIVERTED BACK TO DEN. (FLT#5849) CLOSED REMOVED AND REPLACED NLG SELECTOR VALVE IAW AMM. VALVE LEAKS CHECKS GOOD.