What causes a toilet to automatically start and stop running without being flushed?
Most toilets are controlled by float valves that start filling
the tank when the water level drops. If the toilet is filling
repeatedly without the toilet being flushed, then your problem is
the stopper flap that is located at the bottom of the water tank on
the back of the toilet. It probably has a small leak that is
causing the water level to drop, which causes the float to fall,
therby opening the fill valve which refills the tank after a flush.
Try to see if the chain that is attached to the handle is stuck in
the opening, or if there is some obvious reason why the flap is not
sealing properly. Your problem can most likely be fixed by
replacing the flap valve. 545Bad flapper. Easy to repair, no