Why Does My Toilet Keep Running?

Introduction

A toilet that keeps running can be frustrating and wasteful. You may hear a constant trickling sound, notice the cistern refilling repeatedly, or see water flowing into the bowl long after flushing. While the toilet may still appear to work, a running toilet is a sign that something inside the cistern is not functioning as it should.

This article explains why a toilet keeps running, how the internal parts work, and what typically causes the problem. It is written in clear UK English and is suitable for beginners with no plumbing experience.

What Does “Running” Mean in a Toilet?

A running toilet means water continues to flow into the bowl or cistern after the flush cycle should have ended. This can happen continuously or intermittently, with the cistern refilling at random intervals.

In most cases, the issue is caused by a problem with one of the internal components inside the cistern.

How a Toilet Is Meant to Work

The Cistern and Its Components

A toilet cistern contains several key parts that control flushing and refilling:

Fill valve (also called the inlet valve)
Float or float cup
Flush valve
Seal or washer
Overflow pipe

These components work together to stop water flow once the cistern has refilled to the correct level.

What Happens During a Normal Flush

The flush mechanism lifts the flush valve.
Water flows from the cistern into the bowl.
The flush valve closes.
The fill valve opens and refills the cistern.
The float rises and shuts off the fill valve.

If any part fails, water may continue flowing.

Common Reasons Why a Toilet Keeps Running

Faulty Flush Valve Seal

The most common cause of a running toilet is a worn or damaged flush valve seal.

When this seal does not sit properly:

Water leaks slowly into the bowl
The cistern never reaches the correct level
The fill valve keeps refilling the tank

This creates a continuous or repeated running sound.

Float Set Too High

The float controls when the fill valve shuts off.

If the float is set too high:

Water rises above the correct level
Excess water flows into the overflow pipe
The fill valve continues to run

This often results in a steady trickling noise.

Worn or Faulty Fill Valve

The fill valve controls water entering the cistern.

Problems include:

Internal wear
Debris preventing a proper seal
A valve that does not close fully

This causes water to keep flowing even when the cistern is full.

Overflow Pipe Issues

The overflow pipe prevents the cistern from flooding.

If water flows into it constantly:

The water level is too high
The float or fill valve is not shutting off
The toilet will continue to run

Flush Button or Handle Sticking

A flush mechanism that does not return properly can keep the flush valve open.

This may be caused by:

A stiff or misaligned button
A loose or tangled linkage
Wear in the mechanism

Even a slight gap can allow water to leak continuously.

Limescale Build-Up

In hard water areas, limescale can interfere with moving parts.

It can:

Prevent seals from closing properly
Restrict float movement
Cause valves to stick

Over time, this leads to persistent running.

Incorrectly Fitted Components

If parts inside the cistern are misaligned or poorly fitted:

Seals may not seat correctly
The float may jam
The flush valve may not close fully

This often happens after repairs or adjustments.

How to Tell Where the Problem Is

Listen for the Sound

Different sounds can point to different issues:

Constant trickle into the bowl suggests a flush valve leak
Continuous refilling noise suggests a fill valve issue
Intermittent refilling suggests slow leakage

Check the Water Level

If the water level is:

Above the overflow pipe: float or fill valve issue
Below normal but refilling frequently: leaking seal

Simple Dye Test

Adding a small amount of food colouring to the cistern can help identify leaks. If colour appears in the bowl without flushing, the flush valve seal is leaking.

Practical Examples

Example 1: Toilet Refills Every Few Minutes

Water slowly leaks into the bowl through a worn seal, triggering the fill valve repeatedly.

Example 2: Constant Trickle Sound

The flush valve is not sealing properly, allowing water to pass continuously.

Example 3: Running After a Flush Only

The flush button may be sticking or the float may be catching on another component.

Why a Running Toilet Should Not Be Ignored

A running toilet can:

Waste a significant amount of water
Increase water bills
Cause unnecessary wear on components
Lead to further plumbing issues

Even a slow leak can waste hundreds of litres of water over time.

Frequently Asked Questions

Why does my toilet keep running after I flush?

This usually happens because the flush valve does not close properly or the float is not shutting off the fill valve.

Can a running toilet fix itself?

Rarely. The issue usually worsens as components continue to wear.

Why does my toilet run on and off?

Intermittent running often means water is leaking slowly into the bowl, triggering the refill mechanism periodically.

Is a running toilet expensive to run?

Yes. Even a small leak can significantly increase water usage over time.

Why does my toilet run more in hard water areas?

Limescale can build up on seals and valves, preventing them from closing fully.

Can the flush button cause running?

Yes. A stuck or misaligned button can keep the flush valve slightly open.

Why does water flow into the bowl constantly?

This indicates a leak past the flush valve seal or an overflow issue.

How do I know if the problem is the fill valve or flush valve?

If water flows into the bowl, it is usually the flush valve. If the cistern overfills, it is often the fill valve or float.

When the Problem Might Be More Serious

Seek further investigation if:

Multiple toilets have similar issues
Water backs up or drains slowly
The cistern does not fill at all
You notice leaks outside the toilet

Conclusion

A toilet that keeps running is usually caused by a problem inside the cistern, most commonly a worn flush valve seal, incorrect float level, or a faulty fill valve. While the toilet may still appear to work, ongoing running wastes water and can lead to higher bills and further wear.

Understanding how the toilet mechanism works makes it easier to recognise the cause and take appropriate action before the problem worsens.