To stop it right now
Close the small shutoff valve on the wall behind the toilet by turning it clockwise. The tank will stop refilling until you open it again.
Step by step
- Chain: it should have a little slack when the flapper is closed — adjust it one or two links if it is tight or tangled
- Float: if water is flowing into the overflow tube, lower the float by adjusting its screw or clip so the water stops about an inch below the tube
- Flapper: press it down gently — if the running stops, the flapper is not sealing and should be replaced
- Fill valve: if the float is set correctly and water still flows, the fill valve is worn and can be replaced
Buying parts
Take the old flapper or note the toilet’s make and model when buying a replacement. Flappers come in different sizes, and one that does not fit will not seal.
When professional help makes sense
If new parts do not stop it, the flush valve seat may be damaged or the tank may be leaking elsewhere. A toilet that is also rocking or leaking at the base needs a closer look.