Things You'll Need
New flapper valve
When your Kohler toilet randomly runs or phantom flushes, the cause is a leak in the toilet's tank that is allowing water to flow into the bowl in between flushes. Normally, when you press your Kohler toilet's handle, the handle lifts an arm in the tank, which pulls on the chain holding the flapper valve over the drain hole in the bottom of the tank. A flapper valve may wear out from age or from drop-in tank cleaning tablets, leading to the phantom flushing.
Remove the toilet tank lid and put it in a safe place to avoid damaging the lid. Wait until the toilet is silent and then drop dark-colored food coloring into the tank's water. Watch where the food coloring flows to pinpoint the source of the leak.
Push down on the toilet's flapper with the flat end of a stick if the food coloring leaks past the flapper, waiting until the toilet stops running again. If the toilet stops running, lengthen the flapper's chain by sliding a new link onto the clip that holds the chain on the arm inside the tank.
Close the toilet's water supply valve on the wall by turning its handle clockwise until it stops. Flush the toilet once by lifting up on the flapper's chain, emptying most of the water out of the tank.
Pull the flapper off the hinge pieces on the bottom of the toilet's fill valve and remove the chain from the hook. Press a new flapper that exactly matches the old one onto the hinges on the fill valve and hook the chain onto the clip on the arm, allowing the chain about three links of slack.
Adjust the height of the toilet's float, if the food coloring flows down the overflow tube, by either bending the metal arm that holds the float down or by pinching the clip on the float while you slide the float down. The water inside the tank should sit at least an inch below the top of the overflow tube. Replace the tank's lid and turn the water supply valve handle counterclockwise to restore the water flow to the toilet.