My new Kohler cimmeron toilet won't stop running.

SOURCE: Master bath toilet replaced with a Cimmeron class

Kohler is correct. The most likely cause of this problem is an obstruction in the common vent stack that both toilets share. When you flush the old toilet it need more air to flush and will get it from the easiest source (your new water saver toilet). First adjust the float level in the old toilet so it won't use as much water or just stick a brick in the tank to take up space.Second, run a snake down the vent stack from the roof to check for obstructions. Birds will sometimes nest in there.