: My toilet goes on and off by itself. I can be sitting in a room and all of a sudden, I hear the toilet run, then it stops.And it continually does it.Help Lift the tank cover off the toilet, and flush it, the thing that lifts up and lets the water out of tank, it will be a rubber ball or flapper needs to be replaced.Make sure the seat were the ball or flapper sits on is smooth if not sand it down with some sandpapper. Good luck! Mike C.