A garage door that starts down and reverses is responding to a safety input or mechanical resistance. Misaligned sensors, debris at the threshold, incorrect force or travel settings, and a binding door can all cause reversal. Do not blindly increase force to overpower an obstruction.
Note exactly where the reversal occurs
If it reverses immediately, inspect the sensors and their line of sight. If it nearly reaches the floor first, travel settings, the threshold, or resistance near the end of movement become more likely.
Clean sensors and clear the threshold
Dust, cobwebs, leaves, or a bumped bracket can interrupt the beam. Correct only accessible alignment according to the manual and do not defeat the sensors by pointing them at each other away from their normal installed positions.
Check that the door moves freely
With the opener disconnected only by the manufacturer procedure and the door in a safe position, a balanced door should move without major binding. If it is heavy, crooked, or catches, do not increase opener force to compensate.
Adjust travel limits only by the model procedure
Travel limits tell the opener where to stop. Excessive changes can drive the door into the floor or undermine protection. Follow the manual in small increments and retest safety reversal afterward.