There is nothing like standing in the driveway at night watching your garage door go down, stop, and roll back up for no visible reason. It did that to me for a week before I figured out why. The good news: most of the time this is a simple sensor problem you can fix in minutes, not a broken opener.

The sensors are the usual suspect

Modern garage door openers have a safety system: two sensors near the floor on either side of the door. If the beam between them is blocked or misaligned, the door refuses to close and reverses instead. Something as small as a leaf, a cobweb, or a box sitting in the path can trigger it. Look at both sensors. Most have a small light that should be solid. If one is blinking or off, that is your problem.

Clean and realign the sensors

First, wipe the lenses with a dry cloth. Dust and spider webs block the beam more often than you would think. If cleaning does not fix it, loosen the wing nuts holding a sensor and adjust its angle until the light turns solid. They need to point directly at each other. Sometimes a bumped sensor shifts just a fraction and that is enough to break the beam. Once the lights are solid on both sides, try the door again.

Check the tracks for junk

If the sensors are fine and the door still reverses, inspect the tracks on both sides. Rocks, gravel, or a bent track section can make the door think it hit something. Look at the rollers and make sure nothing is stuck. Wipe a little lubricant on the rollers and hinges if they look dry. A door that binds anywhere along the track will reverse because the opener senses extra resistance.

The close force setting

Most openers have a force adjustment that controls how hard the door pushes to close. If the force is set too low, the door reverses on its own because it thinks it met an obstacle. There is usually a small dial or button on the opener unit labeled with force or travel adjustments. Turn the close force up slightly and test. Do not crank it to maximum, since the safety reverse exists to protect pets and people.

When to call a pro

Some causes are not DIY friendly. If the door reverses only partway down, if the springs look damaged, or if the opener motor strains, stop and call a garage door technician. Springs are under serious tension and can cause injury. A reversing door is annoying, but a door that falls is dangerous. When in doubt, get a professional look.

My fix turned out to be a sensor that had been nudged by a broom leaning against the wall. Thirty seconds with a screwdriver and the light went solid. The door has closed cleanly every night since. Check the simple things first, they are usually the answer.