2. The safety sensors may need adjustment or realignment. Near the bottom of the door track on both sides are electronic eyes that require a clear line of view between them. If the sightlines are clear between the eyes, the door will close smoothly all the way to the floor. However, if anything is blocking the sightline, or if the brackets holding the electronic eyes are out of alignment, the door will fail to descend all the way. In most cases, the door will stop or reverse, and lights will flash to tell you there is a problem. 
They sent Doug Fussell out to my house on the day after Christmas! I had only called them three days before! Doug was a premier technician, very thorough and very efficient. I expected him to take two days, since he was replacing two doors and adding openers on each door. He only took the daylight hours of one day! I could not believe how fast he was! In addition, he thoroughly taught me how to use the remote openers. I highly recommend them to anyone!

Garage Door Opener