Garage door will not close? Sensor repair and the other causes
A door that reverses before it lands is usually reporting a problem with its safety sensors, not with itself. In Los Angeles there is one cause to rule out before any of the others, and it only happens for an hour or two a day.
What the door is telling you when it comes back up
An opener will not close a door it believes something is underneath. Two photo-eye sensors sit within about six inches of the floor, one each side of the opening. One sends an infrared beam across, the other receives it. Break that beam, or give the receiving eye reason to doubt it, and the door stops and comes back up. On most units a light on the motor head or on a sensor blinks to report it.
The Los Angeles version: late afternoon sun
If your driveway faces west, there is an hour or two when the sun sits low and shines straight down the opening. Sunlight carries plenty of infrared, and it can swamp the beam the receiving eye is watching for, so the opener reads clear air as an obstruction. The pattern gives it away. It closes all morning, reverses between about four and seven, then closes normally again after dark. Shading the eye, or turning it out of the light, usually settles it.
A blocked, bumped or filmed-over sensor
Start at the floor. A recycling bin, a coiled hose, a bike wheel, a stack of boxes that slumped overnight. Then the eyes themselves. Garages here collect a fine dry dust, and closer to the coast the marine layer leaves a film on the lens that can weaken the beam. A knock from a car door or a handlebar can rotate a bracket two or three degrees, plenty to lose alignment across a sixteen-foot opening. Lined up, both units show a steady light.
Wiring that has been there for years
The sensor wire is thin, usually stapled along the wall, and it has had a long time to go wrong. A staple driven too tight, brittle insulation at an old splice, or rodent damage can produce the same blinking light as a misaligned eye.
Sensors clear, and it still comes back up
Next comes the travel limit. The opener stores how far down closed is. If that setting drifts, the door presses into the floor and reads the resistance as something in the way, or it stops short. Worn rollers or a pinched track can do the same by making it drag on the descent. Limit and force are part of the door's safety system, not settings to judge by feel.
When it is not the sensors
A door that will not lift, or that shows a clear gap in the coiled spring above the opening, has a spring fault. One sitting crooked in its opening, or with a cable slack off the drum, is off its track. Do not force either one. A torsion spring holds a great deal of energy, and a door off its track can drop. Read broken spring or off track and cable, then leave it where it stands and call. If the motor runs and nothing moves, see opener runs but the door does not move, and the rest are on the problems page.
Having us look at it
A door that will not close leaves the garage standing open, which is one of the failures covered under emergency garage door repair. On a sensor repair our technician lines up or replaces the eyes and checks the wire back to the opener before touching the limit settings. The inspection and estimate are free whether or not you go ahead, and a replacement sensor goes on the invoice with its specification.
Ask for a free estimate, or describe the fault to us. We work across Los Angeles County.
Get the door looked at.
The price is written down before anything is touched, and it holds. Nothing else is done without your say-so.