Running Toilet: Causes and How to Fix It

By Ishaq Hassan. Updated October 3, 2026. 3 min read.

Short answer: A running toilet is usually caused by a worn flapper, a chain that is too short or tangled, a fill valve set too high, or water spilling into the overflow tube. Lift the tank lid to see which one it is. Most fixes are simple, low cost parts, and fixing it quickly saves a lot of water.

A toilet that keeps running, hisses or refills on its own is wasting water, sometimes a lot of it each day. The good news is that a running toilet is one of the easiest plumbing problems to fix.

How a toilet tank works

When you flush, the flapper at the bottom of the tank lifts and water flows into the bowl. The flapper then drops and seals, and the fill valve refills the tank until the float reaches the set level. A running toilet means water is leaking past the flapper or the fill valve is not shutting off.

Illustration of a copper pipe joint spraying water onto a stained wall — Leaking joints can soak walls and floors before anyone notices.

Find the cause

Take the tank lid off and watch after a flush.
If water spills into the tall overflow tube, the fill level is too high.
If the tank slowly empties and refills, the flapper is leaking.
Put a few drops of food coloring in the tank. If color appears in the bowl within 15 minutes without flushing, the flapper leaks.
Check the chain between the handle and the flapper. It should have a little slack.

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Common fixes

Adjust the chain: too short keeps the flapper open, too long can get caught under it
Replace the flapper: worn rubber flappers are the most common cause, and replacements are inexpensive
Lower the float: adjust the float so water stops about an inch below the top of the overflow tube
Replace the fill valve: if it keeps running or hisses after adjusting
Clean mineral buildup: on the flush valve seat, which stops the flapper sealing

Illustration of a sink full of standing water that will not drain — A drain that will not empty often means a blockage further down the line.

When to call a plumber

Water leaks around the base of the toilet
The tank or bowl is cracked
The shut off valve behind the toilet leaks or will not turn
You have replaced parts and it still runs
Several toilets or fixtures have problems

A leak at the base can mean a failed wax ring, which can rot the subfloor. Read about plumbing services and toilet overflow cleanup.

Illustration of a rusty water heater leaking into a puddle on the floor — Rust streaks and water around the base mean a water heater may be failing.

Illustration of a leaking pipe dripping under a kitchen sink with a wrench and plunger nearby — Small drips under a sink can damage cabinets and floors over time.

Quick answers: running toilet

Why does my toilet keep running?

Usually a worn flapper, a chain problem, a fill valve set too high or a failing fill valve.

How do I test for a toilet leak?

Put food coloring in the tank. If color appears in the bowl within 15 minutes without flushing, the flapper leaks.

How much water does a running toilet waste?

It can waste many gallons a day, sometimes hundreds, so fix it quickly.

Can I fix a running toilet myself?

Often, yes, by adjusting the chain or float or replacing the flapper or fill valve.

Who fixes toilets?

A plumber. Sifixit can connect you with a local plumber.

This guide covered running toilet. For more background, see the EPA’s WaterSense program, and if you need help, Sifixit can connect you with a local provider.

This guide is general information for homeowners, not professional, insurance or safety advice for your situation.

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