Why Your Toilet Keeps Running, and How to Fix It

A toilet that runs on and off, or never fully stops, is usually one of a few simple internal parts, and diagnosing which one saves an unnecessary repair.

The Flapper

A worn or misaligned flapper is the most common cause. It fails to seal completely, letting water trickle from the tank into the bowl continuously.

The Fill Valve

If the fill valve doesn't shut off at the right water level, it can overflow into the overflow tube, which sounds like running water even though it's a different part failing.

The Chain

A chain that's too short holds the flapper slightly open; too long, and it can get caught under the flapper, both causing a partial seal.