The bottom of the flush valve on a toilet is attached to the water supply through a hose. The flush valve has a float that drops when the toilet is flushed, draining water from the tank through a hole in the bottom. As the tank refills, the float moves up on the flush tower and shuts off the water when it reaches the proper level. If the flush valve runs and does not shut off, it may be stuck or come out of adjustment.
Remove the top of the toilet tank and locate the flush valve on the left side of the tank.
Flush the toilet and watch the float on the flush valve. Determine if the flush valve is getting stuck or if has reached its limit before the water shuts off.
Locate the adjustment screw on the top of the float and turn it counterclockwise with a screwdriver if the float does not stick. This will drop the float so it shuts off the water at a lower level. Turn the screw a quarter turn at a time and flush the toilet in between to determine when the float is at the proper adjustment.
Spray the float and the flush tower with a lubricant if the float seems to be sticking. This will allow the float to move along the tower more smoothly. Replace the tank top and flush the toilet to test the repair.