A running toilet may seem minor, but it wastes gallons of water and adds up to higher bills. This guide shows you how to diagnose, repair, and maintain the most common causes in three careful stages. In Chapter 1, you learn how to map the inside of the tank, identify parts like the flapper, float, and fill valve, and run a dye test to prove the source of the leak. Safety steps—such as shutting off water, protecting the porcelain lid, and working with dry hands—are emphasized. By the end, you can tell whether the problem is a leaking flapper, an overfilled tank, or a fill valve that won’t close. In Chapter 2, you carry out the actual repairs. You replace a worn flapper with the correct size, adjust the float to keep water one inch below the overflow, or install a new fill valve if needed. Each step is broken into simple checks, with chain slack, refill tube routing, and quiet shutoff all verified by tests. In Chapter 3, you confirm long-term success. An overnight dye test ensures no hidden leaks. Troubleshooting covers ghost flushes, weak flush strength, and hard water scale. A maintenance plan helps you inspect every three months, wipe the flapper seat, and replace parts on schedule. By following these steps, anyone can stop a running toilet safely, save money on water bills, and gain lasting confidence in DIY plumbing.