Kohler toilets flush using a series of components housed inside the tank of the unit. The handle of the toilet attaches to a flapper at the bottom of the toilet tank. When the handle is pressed down, the flapper lifts up, releasing water from the toilet tank into the toilet bowl. The fill valve of the toilet then begins to add water to the tank to refill it for the next flush. As the water level rises, a float ball rises. New Kohler models use a fill valve that has a rising float attached to the bottom instead of the float ball. Once this device lifts, the water supply stops. If the toilet keeps running, one of these pieces likely needs replacing.
Remove the top of the toilet tank by lifting up. Set it aside carefully since it is breakable.
Press down on the flapper at the bottom of the toilet tank and listen for the water to stop. The flapper needs replacing if the running water sound stops.
Turn off the water supply to the toilet at the shut-off valve behind it by turning the handle clockwise. Press down on the toilet handle to remove water from the unit.
Disconnect the chain from the flapper. Lift the flapper up and off the hook it rests on. Replace the flapper. Test the unit and continue troubleshooting if the unit continues running.
Gently bend the rod that the rubber ball sits on so that it rests 1 to 2 inches below the top of the overflow pipe in the middle of the unit. Turn on the water supply and allow the water to refill the tank. Flush and see if the water stops running. If it doesn't, you need to replace the fill valve.
Turn off the water supply and flush the unit. Set a bucket under the water supply line leading to the toilet. Turn the nut holding the water supply line to the toilet and remove the supply line.
Turn the nut on the inside of the unit holding the fill valve in place. Pull the fill valve out of the unit. Insert a new fill valve into the hole and tighten it down. Adjust the fill valve by turning its head until the critical level mark on the fill valve body is just below the overflow pipe. Turn on the water and flush to test.