Toilet Running Constantly: Causes, Fixes & Costs 2026

Who this is for: Homeowners who hear their toilet refilling itself every few minutes — or running nonstop — and want to know whether this is a $4 flapper swap, a $280 plumber call, or a sign of a bigger plumbing problem hiding in the walls.

A constantly running toilet wastes 1–4 gallons per minute — that's 1,440–5,760 gallons per day, or $30–$200 per month on your water bill in 2026. The cause is almost always one of five $4–$40 parts inside the tank that you can replace yourself in 15–25 minutes with no special tools. The flapper is the culprit in 70% of cases. If your toilet is over 25 years old or you've replaced parts twice in two years, the smarter move is replacing the entire toilet for $280–$680 installed and getting a 3× water-efficiency upgrade in the process.

Every toilet has the same simple cycle: you flush, the flapper opens, the tank empties into the bowl, the flapper drops back into place, the fill valve refills the tank, and a float shuts the fill valve off. A toilet that runs constantly is failing one of those four mechanical steps. Either the flapper isn't sealing (water leaks from tank into bowl, fill valve keeps topping off), the float is set too high (water spills into the overflow tube continuously), the fill valve itself is stuck open, or the chain/handle is hung up keeping the flapper open.