Toilet Running Basics

Common causes and safe first checks when a toilet keeps running after flushing.

A running toilet is frustrating but very common. It usually comes down to one of three simple parts — and you can check them safely without special tools.

This guide is for general education only. If water is leaking onto the floor, the shutoff valve is not working, or you are unsure of anything you see inside the tank, contact a qualified plumber before proceeding.

What Does "Running" Mean?

A running toilet means water is continuously flowing inside the toilet — either into the tank or into the bowl — without anyone flushing it. You may hear a hissing, trickling, or gurgling sound. This wastes a significant amount of water and can increase your water bill.

Three Most Common Causes

Worn flapper

The rubber flapper at the bottom of the tank seals the opening to the bowl. When it wears out or warps, water slowly leaks from the tank into the bowl continuously.

Float set too high

The float controls the water level in the tank. If it is set too high, water overflows into the overflow tube and runs into the bowl non-stop.

Fill valve problem

The fill valve refills the tank after a flush. When it wears out, it may not shut off properly, causing the tank to keep filling or hissing.

Safe First Checks

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Listen: is water running into the tank or into the bowl continuously?

Remove the tank lid carefully and set it flat on a stable surface

Check the water level — is it above the top of the overflow tube?

Watch the flapper at the bottom — does it seal fully after the tank fills?

Gently lift the float ball or float arm and see if the water stops

Check the chain attached to the flapper — is it tangled, kinked, or too short?

Do not force or overtighten any plastic parts inside the tank

Replace the tank lid carefully when done inspecting

If water is on the floor — call a plumber before doing anything else

The Dye Test (Optional)

To check for a leaking flapper, add a few drops of food coloring to the tank water. Wait 10–15 minutes without flushing. If color appears in the bowl, the flapper is leaking. Flush after the test to clear the color.

Know When to Call a Pro

Call a qualified plumber if any of these apply:

▸Water is leaking onto the floor around or behind the toilet
▸The shutoff valve (behind/beside the toilet) is not working or is leaking
▸The toilet is rocking or feels unstable
▸You see cracks in the porcelain bowl or tank
▸The problem keeps returning after a simple fix
▸You are not comfortable removing or replacing internal parts
▸There is a sewage smell near the toilet

See full safety guide →