The short answer to this would be “call a plumber.” But we don’t expect you to accept this at face value—we’ve gone into more detail below on what exactly might be causing this problem, and what can be done about it.
A running toilet is a nuisance to listen to, and can also cost you significantly in excess water you aren’t using—something that will reflect on your monthly water bills. A running toilet also means you have an inability to flush. Be sure to call for system repairs as soon as you notice this problem. In the meantime, read on for a further explanation.