This tends to happen because the toilet flapper is worn out, cracked, broken, or dislodged.

What Is a Toilet Flapper?

Remove the old flapper, and replace it according to the manufacturer’s directions.

Empty toilet tank

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When everything works correctly, water will rise to the set level, then stop filling the tank.

This opens up the flapper, letting the water in the tank rush into the toilet bowl.

First, open up the tank and check the lever and chain’s positions, and adjust if needed.

Brass float rod gently bent to increase water flow in toilet diaphragm ballcock

The Spruce / Kevin Norris

If you find the lever is bent or broken upon inspection, replacing the lever is relatively easy.

Simply unscrew and remove the damaged lever, then install a new compatible lever.

Some toilet tanks may even have a line indicating how much water should be inside.

Red flapper attached to pegs on side of flush valve and pressed down in water

The Spruce / Kevin Norris

Adjusting water level to below toilet tank’s overflow tube with brass diaphragm ballcock

The Spruce / Kevin Norris

Flushing Toilet

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Hand checking for leaks behind reinstalled water supply tube to toilet tank

The Spruce / Kevin Norris

Shutoff valve on underside of toilet turned to shut off water

The Spruce / Kevin Norris