You can fix this
Likely cause: a worn or stuck fill valve
If the water keeps running even with the float lifted, or the tank refills with no dye in the bowl, the fill valve is not shutting off. Replace it.
Why this happens
Korky says water that keeps running after the tank is full is a sign the float may be stuck or malfunctioning. When lifting the float does not stop the flow, the valve itself is no longer closing. Korky also offers a simple check: mark the water level after a flush, shut off the supply, and wait at least 25 minutes; if the level drops below the mark, a part inside the tank is leaking.
How to fix it
- Turn off the toilet's supply stop and flush to drain the tank. Sponge out the rest.
- Disconnect the supply line under the tank and unscrew the locknut that holds the fill valve.
- Lift out the old fill valve and install the new one per its package. Set its height so the water level ends up 1/2 inch to 1 inch below the top of the overflow tube.
- Connect the fill tube to the valve nipple and clip it to the overflow tube with its angle adapter, as Family Handyman describes.
- Turn the water on, check for drips under the tank, and test-flush.
When to stop. Water at the base of the toilet or under the tank is a separate leak. Shut the supply stop and call a plumber if you cannot find it.
If this does not fix it, tell the plumber
- The water keeps running with the float lifted.
- Whether there is any water on the floor or under the tank.
- Whether you replaced the fill valve and what happened.
Build the full list: what to tell the plumber.
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