I have a garage door opener that has been working fine until the past month or so. Now, during a close cycle, once it hits the floor (where normally it would stop) it will switch back into an open cycle. It's created several 'Ack I left my garage door open' incidents until I figured it out! Any idea what would cause this? It's about 5 years old, installed it myself.
This is most likely due to the auto reversing function. This is where the door will reverse open if it hits an obstacle when closing.
One possible cause is that there is an obstruction on the floor where the door meets the floor. Look for any irregularities on the floor and on the bottom of the garage door. You might find something stuck to the bottom garage door seal.
Another possible cause is that the door got out of adjustment. Most door I have seen have four adjustments; 1) Open force; 2) close force; 3) open travel distance; and 4) close travel distance. I would look at making adjustments to the close travel distance.
Some, especially Craftsman have limit switches mounted on the chain rail. These have a bad habit of creeping, and would cause this problem. Otherwise, the problem is probably with the sensitivity adjustments as mentioned in last post.
If you have sensors on either side of the garage door, clean them and make sure nothing is obstructing the two from communicating with each other. Perhaps look for something under the garage door (rubber insulation) that may be hanging and obstructing the sensors before the garage hit the floor.