Photo-Eye Sensor Alignment or Replacement: getting ready

There are no sensors at the floor at all, or a previous owner has wired the pair together up beside the motor so the beam never crosses the doorway. A home inspector has just pointed it out.

Worth answering before the call

What make and model is on the opener's label, and roughly how old is it? Does it happen at all hours, or mainly on bright mornings or late afternoons? When did it begin, and what was different that week: a bump, new shelving, a storm, a frost?

How high off the floor should the sensors sit?

Low. The industry checklist expects the beam no more than roughly 15 cm (6 in) up from the floor, so that a small child, a pet or a bicycle wheel breaks it. Both sensors are set at the same measured height and level with each other, since a difference of a couple of centimetres is enough to lose the beam. Within that rule the technician can raise them a little to keep them out of the strip where slush collects.

Why does my door start to close and then go straight back up?

Often the opener believes something is in the doorway, which happens when the receiving sensor stops seeing the beam, whether from an object in the path, a bracket knocked out of line, a dirty or frosted lens, sun in the receiving eye, or a damaged wire. Binding, a force setting or the door arm can cause the same symptom, so the sensor lights and the opener's flashing pattern are read first, and the technician fixes the cause they point to rather than guessing.