Symptoms
- Water keeps running well past when the tank should be full
- Water spills into the overflow tube continuously
- Jiggling the float sometimes stops it temporarily
- Toilet runs nonstop until the water is shut off manually
Likely causes
- CommonWorn valve seal or washerThe internal seal that should stop water flow has degraded and no longer closes fully.
- CommonDebris stuck in the valve mechanismSediment can lodge in the valve, preventing it from sensing the float position correctly.
- PossibleFloat stuck or waterloggedAn old float-ball design can fill with water and sink, never signaling the tank is full.
- PossibleBroken linkage between float and valveA disconnected or bent float arm can't trigger the shutoff.
What to do
- Turn off the shutoff valve immediately to stop the running while you diagnose it.
- Remove the tank lid and check the float for damage, waterlogging (shake it to listen for water inside), or a disconnected arm.
- Reconnect or straighten the float arm if it's loose or bent.
- Turn the water back on briefly and jiggle the float by hand to see if that triggers a proper shutoff, which points to internal debris or wear.
- Replace the fill valve entirely if the float is damaged or the valve doesn't respond correctly, since this is usually more reliable than trying to repair the internals.
Tools and parts
- Adjustable wrench
Toilet fill valveSearch: “universal toilet tank fill valve”
When to call a pro
A plumber isn't usually needed for a fill valve replacement, but call one if the shutoff valve itself is also failing.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.