"Andy" wrote in message
...
The garage door at my mother's house has an intermittent problem.

Sometimes it won't close. If I hold the button down, the door will go
down but when I let go of the bottom it starts going back up.

There isn't anything blocking the sensor.

The garage door opener is a Genie screw drive type that is about 15
years old.

What can I look for to diagnose the problem.

Thanks.

There are sensors that shut off the motor when it reaches a certain point of
travel. These are mechanical switches on top of the track, or an internal
one that adjusts with a + or - symbol over a plastic screw. Get on a
ladder, and work the door. Watch it travel, and look for the limit
switches, as they are called. They are simple metal tabs on top of a box
about one inch square. Once you get up there, if they are there, you will
spot them, just look towards the ends of the track about a foot in. One may
be boogered up. They hold to the track with a simple screw, and that is all
that is necessary to move one to the proper place where it will stop either
the up or down of the door.

Steve