My garage door started closing partway and then rolling back up. It did it for a week before I looked into it, because I was sure it would be expensive. The fix cost me nothing and took ten minutes.

Most garage doors that refuse to close are stopped by the safety sensors, not by a broken door.

The usual cause: misaligned sensors

Garage doors have two small sensors near the floor, one on each side of the door. They send a beam across the opening. If the beam is broken, the door assumes something is in the way and reverses. That is a safety feature, but it also means a dusty or bumped sensor stops the door from closing.

The ten-minute fix

1. Clean the sensor lenses with a dry cloth. Cobwebs and dust block the beam.
2. Check the alignment. The sensors should face each other directly. If one got bumped, loosen its bracket, aim it at the other, and tighten it back.
3. Watch the indicator light. Most sensors have a small light that stays solid when the beam is clear and blinks when it is blocked.
4. Clear the track. Debris in the track can also trigger the safety reverse.

My fix

A storage bin had been bumped against the sensor on the right side. Moving the bin away and wiping the lens fixed it instantly. The door has closed perfectly since, and I had put off the repair for a week over nothing.

Other things to check

If the sensors are clean and aligned, look at:

• The tracks. Dents or buildup can catch the rollers.
• The spring. If the door feels heavy or jerky, the spring tension may be off. Springs are dangerous, so call a pro for that one.
• The limit settings. If the door closes but does not touch the floor, the close-limit setting needs a small adjustment.

When to call a pro

If the door reverses for no obvious reason, or if you see a sagging spring or frayed cable, do not mess with springs or cables yourself. They are under serious tension and can cause injury. Call a garage door company.

I was one storage bin away from a service call. Check the sensors first.