I have a Kohler canister valve toilet that is 3-4 years old. I used it this morning shortly before leaving for work. A few minutes after it finished flushing, I was back in the bathroom to finish getting ready and it started running. Since I needed to get to work, I turned off the water supply and left. When I returned home, I turned it on and it didn't run. I flushed it and it ran, stopped, and was fine all evening. Then I used it again, it finished flushing, and I went to do something else. I came back and it was running. It stopped after 15-20 seconds but it was still dripping consistently inside the tube connected to the flap. Flushing it again caused it to stop running.
I'm assuming that some part needs to get replaced, but not sure what. I did replace the gasket on the valve about a year ago.
Best Answer
Usually you can adjust the float so that it shuts off at a lower water level. Also, sometimes the float is just getting stuck (and it needs to be cleaned).
Edit: If adjustment or cleaning does not work, then you need to replace the fill valve (it's not an expensive part).
Edit2: Reiterating Ed Beal's comment- you may want to start with turning off the water to the toilet and flushing the water out. Then you can inspect or replace the fill valve. A fill valve kit can currently be had for under $10.