How it works
Common causes include a worn flapper, tangled chain, incorrect float height, dirty valve seal, or water level reaching the overflow tube. The fill valve then repeatedly replaces lost water.
What people often miss
Food coloring in the tank can reveal a silent leak into the bowl. Shutoff valves and parts vary, so follow the fixture manufacturer's instructions before disassembly.
Why this question comes up
A small continuous leak can waste a surprising amount of treated water.
Key points
- A toilet keeps running when water continues leaking from the tank into the bowl or the fill system does not shut off correctly.
- Common causes include a worn flapper, tangled chain, incorrect float height, dirty valve seal, or water level reaching the overflow tube. The fill valve then repeatedly replaces lost water.
- Food coloring in the tank can reveal a silent leak into the bowl. Shutoff valves and parts vary, so follow the fixture manufacturer's instructions before disassembly.
Bottom line
A toilet keeps running when water continues leaking from the tank into the bowl or the fill system does not shut off correctly.
Source and verification
This Answer was checked against U.S. Environmental Protection Agency WaterSense. Follow the source for the full official explanation and any later updates.