Garage door sensor works only sometimes?

Intermittent means something changes between the good times and the bad times. Light is the first thing to check. Sunlight shining straight into the receiving eye can overwhelm it, and that happens in a narrow window each day, at a specific angle, which is why it works in the morning and fails at 4 p.m. A short tube or visor on the receiving eye often helps, but it must not block the beam.

Next are the little things that appear and disappear. Spiders love the warm lens of a sensor and can spin a web across it overnight. Dust, frost and condensation can also scatter the beam, as can something temporary like a bin pushed near the door. Each of these clears up on its own, which makes the problem feel random.

Then mechanical causes. A sensor mounted on a bracket that vibrates with the door can drift out of alignment a little each time. Brackets bolted loosely to the track or wall can shift when the door slams. Height matters too. The sensors are meant to sit low, usually around 4 to 6 inches above the floor, so a child or pet is seen; mounted too high they miss things, and mounted at an odd angle they lose the beam. Last is the wire, where a loose connection acts up with temperature and movement.

Intermittent sensors almost never mean a replacement door or opener. A bracket repair, a better location or a new sensor pair is usually the answer. If the opener itself is acting up, see garage door opener repair.