What is the most common cause of a running toilet leak?

There isn’t one single “most common” cause; a running toilet can stem from different internal parts and needs a proper diagnostic. We start with our Gold Star Diagnostic Protocol to identify the root issue, then present repair, rebuild/refresh, or replacement options. If the toilet is overflowing or backing up, we handle it 24/7. Our diagnostic is $179 and waived with repair. Toilet replacement typically ranges $750–$1,500+. <br/> Updated: 2025-12-27 <br/> Need help in Garden City, NY? Call (516) 200-4014 or book online. "Found and repaired a bathroom leak that 2 other plumbing companies could not find." — Jordan H.