Check the Fill Valve

Inspect and clean or replace the fill valve if it fails to shut off completely, causing water to trickle into the tank nonstop.

Steps

1. Remove the tank lid and flush while watching the fill valve
2. If the valve hisses or dribbles after the tank is full, lift the float arm by hand; if the water stops, the float needs adjusting rather than the valve
3. If water still flows with the float raised, clean the valve by twisting off the top cap, rinsing the seal and screen under running water, and reassembling
4. If cleaning does not help, replace the valve: shut off the supply, flush and sponge the tank dry, disconnect the supply line, unscrew the locknut, and install a new fill valve per the manufacturer's instructions

Tips

• A universal fill valve like the Fluidmaster 400A ($8-12) fits most toilets and installs in about 15 minutes
• Debris and mineral deposits are the most frequent cause of a fill valve that won't shut off
• Always turn off the water supply before disconnecting any plumbing