Start with what the door is actually doing
The symptom narrows the cause faster than anything else. Nothing at all, a humming motor, a few inches of movement, or a door that opens then reverses each point to a different part of the system.
Nothing happens at all
Check power first: the opener outlet, the breaker, and whether the wall console lights up. If the wall button works but the remote does not, it is a remote or receiver issue, not the door.
The motor runs but the door does not move
Either the trolley has been disengaged by the emergency release cord, or the opener's drive gear has stripped. Re-engaging the trolley is safe to try; a stripped gear needs service.
The door lifts a few inches and stops
This is the classic broken-spring symptom. Look at the torsion spring above the door: a two- to four-inch gap in the coil confirms it. Do not keep trying the opener — leave the door closed and call for service.
The door opens but reverses immediately
Safety sensors or force settings. Clean the photo-eye lenses, check both indicator lights are steady, and make sure nothing is blocking the beam. If the lights blink, the sensors are misaligned.
The door is crooked or stuck at an angle
A cable has come off its drum or snapped. Stop using the door entirely. Running the opener from here usually damages the top sections and the track.
What not to do
Do not adjust torsion spring tension, do not force a jammed door, and do not disable the safety sensors to make the door close. Those three actions cause most of the serious injuries associated with garage doors.
