# Toilet keeps running: how to fix it

Updated: 2026-10-24 · https://pros411.com/en/guides/plumbers/toilet-keeps-running

## Short answer

Lift the tank lid and look. If water is spilling into the overflow tube, lower the float until the water stops about 1 inch below the top of the tube. If not, check the chain: it needs a little slack. Still running? Shut off the valve behind the toilet, flush, and replace the flapper with one that matches. A fill valve that hisses nonstop needs replacing.

## How to stop a running toilet

![Cartoon toilet that keeps running, with water spilling into the overflow tube](https://pros411.com/img/guias/toilet-keeps-running.webp)

1. **The tank keeps hissing and running.** Water trickles into the bowl all day, and you pay for every drop. The fix is almost always inside the tank.
2. **Lift the lid: is water going into the overflow tube?.** The overflow tube is the open pipe in the middle of the tank. If water spills into it, the water level is set too high.
3. **Lower the float.** Turn the adjustment screw on the fill valve or slide the float clip down. The water should stop about 1 inch below the top of the tube.
4. **Give the chain a little slack.** A chain that is too tight holds the flapper open. Leave about half an inch of slack so the flapper can seal.
5. **Still running? Swap the flapper.** Turn the shut-off valve clockwise and flush to empty the tank. Unhook the old flapper and clip on a new one that matches.
6. **Water back on, and quiet.** Open the valve slowly and let the tank fill. Flush once and listen: no hiss, no trickle.

## Why it happens

- A worn flapper: after a few years the rubber gets stiff or warped and stops sealing.
- The water level is set too high, so the extra water runs down the overflow tube nonstop.
- The chain is too short, tangled or caught under the flapper.
- A worn fill valve hisses and never shuts off fully, even with the water level right.

## Find a silent leak with food coloring

Put a few drops of food coloring in the tank and do not flush. If color shows up in the bowl after 10 minutes, the flapper is leaking. The EPA warns that a worn flapper can silently leak thousands of gallons a year.

## What not to do

- Do not force the float arm or the fill valve: the plastic parts crack.
- Do not use in-tank cleaning tablets with bleach. They wear out the rubber flapper.
- Do not guess the flapper size. Bring the old one to the store: 2-inch and 3-inch flappers do not swap.

## When to call a plumber

- It still runs after a new flapper and the right water level.
- The shut-off valve is stuck or leaks when you turn it.
- Water drips from the supply line or the tank bolts.
- The tank or the ring the flapper sits on is cracked.

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## Frequently asked questions

### Why does my toilet keep running?

Usually a worn flapper that does not seal. It can also be a water level set too high, so water flows into the overflow tube, or a chain that holds the flapper open. You can fix all three inside the tank.

### How much water does a running toilet waste?

A lot. The EPA says a worn flapper can silently leak thousands of gallons a year, and it all shows up on your water bill.

### Can I fix a running toilet myself?

Yes, most of the time. Adjusting the float or the chain takes minutes, and a new flapper clips on by hand.

### How do I know which flapper to buy?

Take the old one to the hardware store. Most are 2-inch or 3-inch, depending on the size of the hole at the bottom of the tank.

### Is a running toilet an emergency?

No, as long as the water stays in the bowl. If the noise or the waste bothers you, close the shut-off valve behind the toilet until you fix it.

## Sources

- [EPA WaterSense: Fix a Leak Week](https://www.epa.gov/watersense/fix-leak-week)