A door that will not close is almost always the safety system telling you it is not satisfied, and the safety system is a pair of small sensors either side of the opening. Start there, because it is the cheapest thing to rule out and by far the most common answer.
Check these first, in this order
- Clear the path between the two sensors — anything at all, including a broom or a cardboard box.
- Clean both sensor lenses gently, including the ones you cannot easily see.
- Check the sensors are level with each other and aimed straight across at about waist height.
- Check the mounting brackets are firm and not bent, and that the units will hold their aim.
- Follow the low-voltage wire from each sensor to the opener and look for a cut or pinched section.
Safety sensor faults: the most common cause by far
The two photo-eyes mounted low on the tracks are what stop the door closing on something. If the beam between them is blocked, or they are not talking to each other properly, the door will not close at all.
- Something in the way. Far more often than people expect. A broom, a leaf pile, a dog, a bicycle, a recycling bin that has been moved too close.
- Dirty lenses. Dust, spider webs, and road film are enough to make the beam unreliable.
- Misalignment. The two units have to be aimed at each other. Plenty of mounting brackets get knocked and never put back properly.
- A bent or loose bracket. If the bracket has given, alignment cannot hold. This is what a car in the driveway does.
- A cut or corroded wire. The low-voltage run between the sensors and the opener, usually where it passes through the jamb.
- A failed sensor. The unit has stopped working, which is more common than most people expect on sensors that have been in a damp garage for a decade.
Most openers flash the courtesy light when the safety path is not satisfied, so that is a quick confirmation if your door has that behaviour.
If the door closes then reverses
A door that reverses partway through closing is the opener detecting an obstruction it cannot see. The causes, roughly in order:
- Misaligned sensors. Still the first thing to check. An intermittent alignment problem produces a door that closes sometimes and reverses sometimes.
- A genuine obstruction on the door. A bent panel, a delaminated section, a bowed door, or something caught in the track. A dirty section of track is enough to cause it.
- Track or roller problem. If the door is not travelling square, it will bind at the same point every time. The clue is that it always happens at the same point in the travel — that points to the door, not the sensor.
- Force setting too low. The opener is being too cautious. Correcting it by forcing the door is the wrong fix; the cause is usually an out-of-balance door.
- A dirty or damaged bottom seal. A hardened or deformed seal can drag and trip the reverse.
That distinction — same point every time, versus random — is the most useful diagnostic you can make, and it saves a lot of time.
If the door stops partway open
A door that will not close all the way is a different problem from one that will not close at all.
- A limit setting that is too high, so the opener thinks it has reached the top before the door has.
- A track that is bent or not plumb, so the door binds at a set height.
- A roller that has come out of the groove on one side, which usually shows up as the door sitting crooked.
- Something catching the bottom of the door — a bin, a box, an uneven driveway lip, or a door that has dropped and is resting on something.
- A door that is no longer square because the frame has moved or a track anchor has loosened.
If the door stops at the same height every time, that is a very specific fault and it is usually mechanical rather than electronic.
What to fix yourself, and when to call
Worth doing yourself, because it resolves a large share of cases:
- Clear the path and clean both lenses.
- Re-align the sensors, and use the courtesy light to confirm the beam is solid.
- Replace a straightened or bent bracket.
- Vacuum the tracks so debris cannot jam a roller.
- Check the bottom seal for hardening, gaps, or a deformed edge.
Call about:
- A damaged or cut low-voltage wire run.
- Failed sensors that are clean, aligned, and firmly mounted.
- A control board fault, once the wiring and sensors have been ruled out.
- Anything bent, off track, or binding at a consistent point.
- A door that will not close and leaves the opening unsecured. That is a security issue and it is worth treating as urgent.
Related services & problems
These usually go together, because the same underlying wear shows up in more than one place.