HOW-TO GUIDES
How to fix a running toilet
Updated 07/26
By: Content Team
Reviewed: Kim Staples
There's nothing worse than a faulty toilet - especially if you only have one toilet in your home. Don't worry, here we'll show you how to fix a running toilet.
Why your toilet keeps running after it's flushed
How to test which part is actually causing the leak
How to fix the fill tube, float, and flapper
What to do if it's still running after those checks
When to call a plumber
Got a toilet that won't stop running? Not only is this annoying, but it can also lead to water wastage and a hike in your water bill. So, you'll want to find a fix as quickly as possible.
The good news is that the cause is usually one of a small handful of well-known parts, and most fixes don't need a full plumbing overhaul.
But remember: if you're in any doubt about your abilities - or you simply don't have the time, tools or experience needed - it's best to call in a plumber. Enter your postcode into the search box below to find a plumber near you.
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Why does my toilet keep running?
If your toilet is constantly running, one of two things is generally happening:
Water is escaping from your toilet tank into the bowl, or
A component inside your toilet cistern isn't sealing properly
Several different issues could cause these problems. Often, though, it's a leaking flapper, a faulty fill valve, or an overflow pipe that's the wrong size.
Luckily, you won't need to replace your whole toilet. Instead, these things are relatively easy to fix.
So how do you fix a running toilet?
Diagnosing it depends slightly on your toilet type - lever handles, push-button systems, wall-hung concealed cisterns, and traditional high-level cisterns are all put together a little differently - but the checks below cover the vast majority of running toilet problems.
Here's how to stop a toilet from running water in just a few steps.
Step 1 - Check the fill tube
First things first, let's rule out your toilet's fill tube.
Remove the tank lid and locate the fill tube. This small, bendy tube goes from the fill valve to the toilet overflow tube.
After each flush, this tube squirts enough water down the toilet overflow tube to refill the bowl while the tank refills.
Make sure it's attached firmly to the fill valve. It should sit about an inch above the top of the overflow tube. If it isn't, push it down firmly onto the fill valve.
Step 2 - Check the water level
Every type of toilet uses some version of a float to sense the water level, which then shuts off the fill valve when the cistern is full with enough water.
It could be a ballcock float, a float cup, or a syphon with a built-in diaphragm. There should also be a marked fill line on the inside back of the tank.
Flush your toilet and check whether the water level reaches and stops at that mark. If it doesn't:
Make sure the water supply valve is fully open
Adjust the float. On older toilets, this usually means gently bending the brass arm. On newer ones, it means turning a screw or sliding a clip along the rod
Step 3 - Check the float
While adjusting the float, it's a good idea to check the float itself to make sure it isn't waterlogged.
Sometimes, floats can become clogged with water, which can cause your toilet to run.
Unscrew the float and give it a gentle shake to see if you can hear water inside it. If you can, you'll need to replace it.
Step 4 - Test the flapper
If your toilet is still running, this could be because the flapper is stuck open. This is the most common cause.
When the flapper opens, this causes the toilet to flush. But if it can't close properly and completely cover the valve, your toilet will continue to run.
Untangle the chain if it's caught, and adjust it so there's only a small amount of slack when the flapper is closed
Trim any excess chain, leaving about an inch of spare, to help prevent future tangling
If the chain is too long, or the flush rod hits the tank lid, the flapper may not lift far enough for a full flush - bend the rod slightly and readjust it
Here's a quick way to check the flapper directly: Reach into the tank and push down on the flapper while the toilet is running. If the water stops immediately, the flapper is your culprit.
Step 5 - Check the flush valve seat
If the flapper looks fine but the toilet still runs, run a finger around the flush valve seat - the rim the flapper rests on.
Rough patches, mineral buildup, or corrosion here stop the flapper sealing even when it's brand new.
Very light buildup can sometimes be smoothed with fine emery cloth, but a damaged or pitted seat usually means you need to replace the whole flush valve.
Step 6 - Flush the toilet
Last but not least, it's time to flush the toilet to find out if your fixes have worked. Fingers crossed, you've managed to stop your running toilet bowl!
If not, however, it's time to look into replacing parts rather than just adjusting them.
Toilet still running? Replace the fill valve or flapper
If you've followed the above steps and your toilet is still running, the likely culprit is your toilet's fill valve or flapper.
These parts can become defective or worn out, in which case, they'll need replacing.
How to replace
Flapper: Turn off the water supply, flush to drain the tank, and unhook the old flapper from the overflow tube. Fit the replacement (matching the size and shape of the old one) and reconnect the chain with a small amount of slack.
Fill valve: Turn off the water and drain the tank, then disconnect the supply line and unscrew the mounting nut to remove the old valve. Fit the new one and reconnect.
Alternatively, if you have a modern push-button toilet, it likely relies on a syphon rather than a flapper - this looks like a cylindrical plastic tower. Again, this can degrade over time and may need replacing.
It's often cheaper to replace just the washer at the base of the syphon, but it can be tricky to confirm that's definitely the fault without opening it up.
How to replace a toilet syphon
Want to know how to replace a toilet syphon? Look no further. Our informative guide will take you through the process step-by-step with tips and costs.
When to call a plumber to fix a running toilet
Although fixing a running toilet might sound simple enough, there are lots of different kinds of toilets and it can be tricky to identify exactly what's going wrong.
It can take an enthusiastic DIYer a lot longer than expected - and there's always a slightly damp risk of ending up with the lid off, the cistern exposed, and no closer to a fix.
For most people, therefore, a job like fixing a running toilet is best handled by a trusted plumber.
A plumber will usually carry the right parts already, and years of experience means they can diagnose and fix the issue much faster than trial and error at home. In the worst case scenario, they may recommend replacing the toilet entirely.
Enter your postcode into the search box below to start searching for a plumber for your job - or download the Checkatrade app.
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How much does it cost to fix a running toilet?
As a rough guide, plumbers typically charge around £50 an hour.
The overall cost you'll pay depends on what's actually wrong - a flapper or fill valve replacement is usually a quick, low-cost job, while a full flush valve or cistern replacement will take longer.
You'll also need to pay the cost of any new parts that are needed.
Plumber costs in the UK: 2026 price guide
Whether you are planning an exciting renovation or have a troublesome issue, our plumber cost guide contains daily, hourly and emergency rates.
FAQs
The answer is almost always a leaking flapper, faulty fill valve, or misaligned fill tube. Occasionally it's high water pressure or an ageing cistern that needs more than a simple part swap.
Add a few drops of food colouring to the tank water and wait 15 minutes without flushing. If the colour appears in the bowl, that confirms the flapper (or the seat it rests on) is leaking.
A running toilet could leak between 200 and 400 litres (50 to 100 gallons) of water per day.
That adds up quickly on your water bill, so it's worth getting it fixed right away.
Possibly, yes. Many running toilet problems are straightforward DIY fixes - it's usually just a case of adjusting the float, chain, or fill tube, or replacing a flapper or fill valve.
If you're not confident with DIY, or if you've tried the above and it's still running, it's worth calling a plumber.
Plumbers typically charge around £50 an hour. Simple part replacements are usually quick jobs, so you may not be paying much more than one hour's worth of time (plus the cost of any new parts).
A full valve or cistern replacement will cost more in time and parts, however - you may be paying for a few hours.
Don't be spooked. "Ghost flushing" is when a toilet flushes briefly by itself with no one touching it. It's usually caused by a slow leak past a worn flapper, which drops the water level enough to trigger a top-up - and therefore a flush.
This usually points to a float set too high, or a fill valve that isn't shutting off properly. Check the float adjustment first, then the fill valve itself if the level still won't stop at the overflow.
No - a running toilet means water keeps leaking into the bowl after flushing, while a toilet that won't flush is usually a different fault. See our toilet flush button guide if that's your issue instead.
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