Why does my garage door open but won't close?

When a garage door opens fine but will not close, the cause is almost always the photo-eye safety sensors near the floor. If they are blocked, dirty, or knocked out of alignment, the opener refuses to close the door and usually reverses it or flashes its lights as a warning. Other causes are a close-force or travel setting that is too sensitive, an object in the door's path, or the wall-button lock feature being on. Start by looking at the small sensors at the bottom of each track for a steady, unblinking light. Here is how to find and fix it.

Check the safety sensors first

Federal UL 325 rules have required photo-eye sensors on residential openers since 1993. These are the two small units mounted near the floor on each side of the door, connected by an invisible infrared beam. If anything breaks that beam, or the opener thinks something does, it will not let the door close, because the system assumes a child, pet, or object is in the way. This is the single most common reason a door opens but will not close.

Look at the lights on the sensors. On most LiftMaster and Chamberlain units, one sensor glows amber or yellow for power and the other glows green when aligned. A steady light on both usually means they are fine. A blinking, flickering, or dark light points to a sensor problem, which lines up with a door that will not close.

Check for the obvious blockers. A leaf, cobweb, box, trash can, or even a car bumper crossing the beam stops the door. Bright sunlight shining directly into a sensor can also fool it; low winter sun at a sharp angle can wash out the receiving eye for part of the day. Clear anything in the path, then try again. If the door now closes, a simple obstruction was the cause, and you are done.

It also helps to know how the system behaves when it refuses to close. On most openers, when the beam is broken the door will not move down at all from the remote, or it starts down and immediately reverses back up, and the opener light flashes several times as a coded warning. If you recognize that flashing-light pattern, the opener is telling you the sensors are the problem, which saves you from chasing the wrong cause.

Clean and realign the sensors

If nothing is blocking the beam but the sensors still misbehave, they are likely dirty or out of alignment. The lenses are small and sit near the floor, so they collect dust, dirt, spider webs, and grime, and a winter's worth of road salt and slush in a Colorado garage builds up fast. Gently wipe each lens with a soft, dry cloth. Do not use harsh cleaners that could scratch the lens.

Alignment is the next check. The two sensors must point straight at each other for the beam to connect. They can get bumped by a car, a bike, or a foot, or knocked loose over time. Loosen the wing nut on the bracket if needed and adjust the angle until the receiving sensor's light glows steady rather than blinking. When both lights are solid, the beam is connected.

Also inspect the wiring. The thin wires running to each sensor can be pinched, cut, stapled too tight, or chewed by pests. A staple driven through a wire is a classic hidden cause. If a light is completely off even after cleaning and aligning, a wiring fault or a failed sensor is likely, which may need a technician.

Look at force settings and the door's path

If the sensors check out, the problem may be the opener's close-force or travel limits. These settings tell the opener how much force to use and how far to travel when closing. If the down-force is set too sensitive, the opener feels normal resistance as an obstruction and reverses before the door seats. If the travel limit is wrong, the opener may think the floor is an obstacle.

A door that starts to close, then stops and reverses before reaching the floor often points to a force or limit setting, especially if it began after a power outage or a settings reset. Most openers have small adjustment dials or buttons for these, and the manual shows how to fine-tune them. Make only small changes, because a force set too high defeats the safety reverse.

Physical resistance can mimic a setting problem. A door that binds on a bent track, a worn roller, or debris in the track meets real resistance partway down, and the opener reverses to protect against an obstruction. Look for anything catching as the door moves. If the door is hard to move by hand, the issue is mechanical, not electronic, and the tracks, rollers, or springs need attention.

When to call a professional

Some causes are quick DIY fixes, and others are not. Try the easy steps first: clear the beam, clean the lenses, realign the sensors until the lights are steady, check that the wall-button lock is off (a lock icon or "vacation" mode disables closing), and look for obstructions in the tracks. These solve the large majority of opens-but-won't-close problems in a few minutes.

Symptom	Likely cause
Door reverses immediately on close	Blocked or misaligned sensors
Sensor light blinking or off	Dirty lens, alignment, or wiring
Closes partway then reverses	Force/limit setting or binding track
Won't close at all, lights flash	Sensor fault or lock feature on

Call a technician when a sensor light stays dark after cleaning and aligning (a wiring or sensor failure), when the door binds on the track or feels heavy by hand, or when adjusting force settings does not help or seems unsafe. The Consumer Product Safety Commission stresses that the sensors and auto-reverse are life-safety features, so never disable them to force the door closed.

A quick word on a tempting shortcut. Some people, frustrated by a door that will not close, hold the wall button down to force it, which on many openers overrides the sensors and runs the door closed without the safety beam. Do this only to get an obviously clear door down in an emergency, and never as a daily workaround, because it bypasses the protection that stops the door on a child or pet. If you find yourself holding the button every time, the sensors need fixing, not bypassing.

Prevention is simple once it is working. Keep the area around both sensors clear of clutter so nothing leans into the beam, and wipe the lenses a couple of times a year, more often in a snowy Colorado winter when salt and grit splash up from the floor. Mount or bump-protect the sensors so a car door or a stored bike cannot knock them out of alignment. A minute of attention now and then keeps the most common cause of a stuck door from coming back, and it is far cheaper than a service call for a problem that was only a dusty lens. G Brothers can diagnose and repair sensor, wiring, and track problems across the Denver metro, with same-day service on most calls.