My LiftMaster garage door won't close all the way and goes back up. What could be causing this?

Your LiftMaster garage door won't close all the way and goes back up due to safety reversal triggered by sensors, limits, force, or mechanical binding, which are designed to prevent injury or damage. Most common cause is misaligned or dirty safety sensors near floor; if beam blocked or green light flashing, door will reverse after closing a few inches. Clean lenses, remove obstructions, and realign sensors until one shows steady amber and other steady green. Second cause is down travel limit set too far, causing door to hit floor and think it hit obstruction, so opener reverses; adjust down limit screw slightly counterclockwise. Third cause is close force setting too sensitive, so friction from cold, lack of lubrication, or bent track triggers reversal; increase close force slightly or lubricate rollers with silicone lubricant and check tracks for bends. Fourth cause is door binding in tracks due to loose bolts, worn rollers, or off-track rollers causing excessive resistance. Fifth cause is broken torsion spring making door heavy, so opener cannot close fully and reverses; check spring for gap. Sixth cause is manual slide lock or handle lock engaged on track preventing closure. Seventh cause is garage floor obstruction like ice or debris. Test manually by pulling emergency release cord and lifting door halfway; if heavy or binding, fix mechanical issue. Reset opener by unplugging 30 seconds.