The garage door will not open
A door that refuses to open is usually a broken torsion spring. The motor will strain, hum, or move a few centimetres and stop, because without spring assistance it is being asked to lift the door's full weight — often more than 100kg on a double sectional. Look at the spring above the door: a broken one has a visible gap, like a spiral cut in half.
The second most common cause is a snapped or derailed lift cable, which leaves one side of the door lower than the other. The third is an opener fault — a stripped drive gear or a failed board — where the motor runs but nothing moves.
Do not keep pressing the remote. Every attempt after a spring or cable failure drags the door further out of square and turns a straightforward spring repair into track and panel damage as well.
The garage door will not close
A door that opens but refuses to close is almost always the safety beams. The two infrared sensors mounted low on either side of the opening must see each other; a spider web, a bag leaning against one, a knocked bracket or a lens covered in dust breaks the beam and the opener refuses to close as designed. Most units flash an error code on the head unit while this is happening.
If the beams are clear and aligned, the next suspects are the down-travel limit setting and the close-force setting on the control board. A door that closes fully and then immediately reverses is being told it has hit an obstruction — usually because the limit is set slightly too low and the door is pressing into the floor.
Broken garage door springs
Springs are the single most common failure point on any garage door because they do the actual lifting. A torsion spring is rated in cycles — typically 10,000 for a standard spring, which is roughly seven years at four cycles a day, and considerably less on a household that runs the door eight or ten times daily.
When one breaks, the door becomes dangerously heavy and unbalanced. Springs are replaced in matched pairs for a reason: both have the same cycle history, and fitting one new spring against one worn spring leaves the door pulling to one side and the survivor failing within months. Full detail is on the garage door spring repair page.