Why does my garage door close all the way then open?

My garage door goes all the way to the floor and comes back up…

If the chain is sagging on the garage door opener there could be several reasons why.

1. Check on top of the garage door opener, the bushing is going bad if you see a black powder residue. If black powder is present, it’s time to replace the gear and sprocket assembly.
2. Check on top of the garage door opener to see if the sprocket (the part the chain is wrapped around) may be leaning or bent. The garage door is very heavy and putting a lot of pressure on the sprocket and eventually that part will break off.  Time to replace the gear and sprocket assembly.

If you are seeing this issue it is time to have your garage door opener serviced by a garage door technician.