A garage door that reverses on the way down or stops in the middle of its travel is giving you clear signs. They point to a few places to look: the safety sensors, the track and balance, or the opener's power and controls. Work through them in that order and write down what you find. Keep hands and fingers out of the track during every check, and do not stand under a door that is held up by hand alone.
Why does the door reverse as it closes?
The safety sensors near the bottom corners of the door send a beam across the opening. If the beam is interrupted, the door reverses. Look for something in the path, such as a bag, a bin, or a low branch in the light. Check that both sensors face each other, that their small indicator lights are steady, and that the lenses are clean. A sensor knocked out of line can often be brought back with a cloth and a gentle nudge to its bracket.
Why does the door stop partway?
A door that stops mid-travel is often being held by the track or the balance. Disconnect the opener first using the release cord, then lift the door by hand from the middle. It should rise and stay roughly where you leave it. If it drops, sticks, or pulls hard to one side, the balance or a track is the likely problem. Do not adjust the springs yourself, and do not use the opener to force the door past the stop. Call the person who services the door, and write down what you saw.
Why does the opener run but the door not move?
Check that the release cord is connected and that the opener is fully seated on its power. Look at the control panel for any blinking pattern, and read the manual's description of what that pattern means. The track and the arm must be attached at their brackets. If the opener hums without moving the door, stop and call for service rather than repeating the attempt.
What to write down
Record what the door did, when the sensors were last cleaned and aligned, and who came out to service it. Those entries help the next person decide whether the problem is in the sensors or in the balance.
Treat the opener's age as a planning input
A door that starts misbehaving is not a verdict on the opener's life. It is a prompt to check the opener against the plan. The garage door opener guide sets out typical service life and when to plan for a change.