The short answer
A running toilet usually means water is continuing to move from the tank into the bowl or overflow instead of shutting off normally. Common causes include a worn flapper, an incorrect water level, a fill valve that is not shutting off, a chain issue, or a damaged flush-valve sealing surface.
Signs you may notice
- Water runs continuously after flushing.
- You hear the tank refill every few minutes.
- Water ripples in the bowl when nothing was flushed.
Possible causes
- A worn or warped flapper no longer seals the flush-valve opening.
- The fill valve is set too high, allowing water to spill into the overflow tube.
- The flush-valve seat is pitted, scaled, or damaged.
- The chain is too tight, too loose, or caught under the flapper.
Safe checks
- Remove the tank lid and watch the water level. If the water rises above the overflow tube, lower the fill-valve float according to the valve manufacturer's instructions.
- Turn off the toilet's supply valve, mark the tank water level, and wait 15 minutes. If the level drops, water is leaking past the flapper or flush-valve seal.
- Inspect the flapper. If it is slimy, warped, cracked, or no longer sits flat, replacement may solve the problem.
When to call a plumber
If a new flapper and fill-valve adjustment do not stop the running, the flush-valve seat may be corroded and need a full flush-valve replacement. Call sooner if the shutoff valve will not close, the toilet leaks onto the floor, or you are not comfortable taking the tank apart.