A UK Guide to Fixing a Toilet Constantly Flushing

That constant hissing or trickling sound from your toilet isn’t just annoying—it’s the sound of water, and your money, literally going down the drain. In almost every case, a toilet that won’t stop flushing is down to a faulty part inside the cistern. The good news? It's usually a straightforward mechanical issue you can often fix yourself.

Understanding Why Your Toilet Won't Stop Flushing

At first glance, the collection of levers and valves inside your toilet cistern can look a bit intimidating. But it’s actually a very simple system. When you flush, a specific amount of water is released into the bowl. The cistern then refills to the correct level and shuts off, ready for the next flush. When your toilet runs continuously, that perfect cycle has been broken.

Nine times out of ten, the problem is something simple and mechanical. You don't need to be a seasoned plumber to have a look and figure out what’s gone wrong.

Getting to Know the Parts Inside Your Cistern

To get to the bottom of the issue, it helps to know who the main players are. Once you pop the lid off the cistern, you'll see a few key components doing all the work:

• The Fill Valve: This is the tall column, usually on the left, that lets fresh water back into the cistern after you've flushed. You'll often hear it working as the tank refills.
• The Float: This is either a ball or a cup-like device attached to the fill valve. It rises with the water level and acts as a switch, telling the fill valve to stop filling once the cistern is full.
• The Flapper (or Flush Valve Seal): Sitting at the bottom of the tank, this rubber seal is what lifts up to let water rush into the bowl when you flush. Its most important job is to create a watertight seal afterwards.
• The Overflow Tube: This is your safety net. It's a tall, open pipe that drains excess water directly into the bowl if the fill valve ever fails, preventing a messy overflow onto your bathroom floor.

When these parts work in harmony, your toilet functions perfectly. But a fault in just one of them is all it takes to cause that non-stop, water-wasting flush.

To quickly figure out what might be causing the problem, it's helpful to see what can go wrong with each part.

Common Culprits Behind a Running Toilet

This table summarises the most frequent causes of a constantly flushing toilet to help you narrow down the issue.

As you can see, a small issue with one of these components is all it takes to start a cycle of constant refilling.

The Financial and Environmental Cost of a Leak

That tiny trickle might not seem like much, but it adds up surprisingly fast. Modern toilets in the UK typically use around 6 litres for a full flush and 3 litres for a half flush. A toilet that runs constantly can waste hundreds of litres of water every single day, leading to a nasty shock when your next water bill arrives. If you want to see just how much water an average UK household uses, you can find more information about UK household water consumption here.

Tackling a running toilet is one of the quickest ways to reduce your home's water consumption. It's not just about saving money on your bill; it's also about conserving a valuable resource.

If you’ve taken a look inside your cistern and the problem seems more complicated than a simple DIY fix, don’t hesitate to call in the professionals. Our expert engineers offer reliable services for a range of home appliance issues, from fixing toilets to handling complex washing machine repairs, ensuring a quick and effective solution.

Your Essential Toolkit and Pre-Repair Safety Checks

Before you even think about lifting that cistern lid to investigate a constantly flushing toilet, it’s worth taking a few minutes to prepare. Trust me, this will make the whole job cleaner, safer, and a lot less stressful.

You don't need a professional plumber’s van full of gear for this. Most phantom flush fixes can be sorted with a few simple things you’ve probably already got in a cupboard somewhere. Getting your tools together first means no scrambling around mid-job.

Assembling Your Basic Toolkit

Here’s a quick list of what you should grab:

• Old Towels: Lay a few of these around the base of the toilet. They’re invaluable for catching any drips and will protect your bathroom floor.
• A Bucket or Sponge: After you’ve flushed the toilet with the water off, you’ll need one of these to get the last bit of water out of the cistern.
• An Adjustable Spanner: This will likely be your best friend for loosening or tightening the nut that connects the water supply line to the toilet.
• A Screwdriver: A simple flat-head or Phillips-head screwdriver is often all you need to adjust float mechanisms or other small fittings inside the cistern.

Once you have these bits and bobs ready, you can move on to the most important safety step.

Before you do anything else, you must shut off the water supply to the toilet. Skipping this will turn a simple fix into a very wet, very fast bathroom flood.

Locating and Using the Isolation Valve

The isolation valve (sometimes called a stopcock) is a small valve that controls the water flow directly to your toilet. You’ll usually find it on the wall behind the toilet or on the pipework leading into the bottom of the cistern. It will either have a small handle or a slot for a screwdriver.

To shut off the water, just turn the handle or the slot a quarter-turn until it’s at a right angle to the pipe. Once that's done, flush the toilet to empty the cistern. You’ll see it doesn’t refill—that’s exactly what you want. It confirms the water supply is off and it's safe to start working.

If you can’t spot an isolation valve for the toilet, you’ll have to shut off the main stopcock for the entire house. Just remember that while you're fixing the loo, none of the other taps in your home will work.

Dealing with persistent plumbing problems can be a real headache. If you've tried the basics and the issue continues, or if you run into something more complex like a boiler malfunction, our experts are here to help. We offer reliable boiler services to keep your home running smoothly.

Getting to Grips With What’s Inside Your Toilet Cistern

With the water safely shut off and the cistern lid carefully set aside, it’s time to play detective. The culprit behind that constant, maddening flushing sound is hiding inside the tank, and a bit of methodical checking is the quickest way to find it. This simple inspection will save you time, frustration, and maybe even a second trip to the DIY shop.

Your first suspect should almost always be the flapper or flush valve seal. This is the rubber disc at the bottom of the cistern that holds water in the tank until you flush. Over time, it’s the part most likely to give up the ghost.

Checking the Flapper for Wear and Tear

Gently run your finger along the rim of the flapper. Does it feel brittle, warped, or chalky? A healthy flapper should be soft and flexible so it can create a perfect seal. Limescale and general decay can cause it to harden and lose its shape, letting water trickle past it into the bowl.

This leak forces the fill valve to keep topping up the cistern, which is what causes that annoying running sound.

There's a simple test you can do. Using a screwdriver or a long stick, lightly press down on the centre of the flapper. If the sound of running water suddenly stops, you've found your problem. This is a dead giveaway that the flapper isn't creating a watertight seal and needs replacing.

Investigating the Fill Valve and Float

If the flapper seems to be in good nick, your next stop is the fill valve and its float. The fill valve's job is to refill the cistern to a specific level and then shut off completely. If it fails, water will just keep pouring in until it spills into the overflow tube, creating a constant flow into the toilet bowl.

A very common issue here is the float height. Ideally, the water level should stop about an inch below the top of the overflow tube. If you see water constantly spilling into that tube, the float is set too high. On most modern UK toilets, this is a straightforward adjustment.

• Float Cup Style: Look for a plastic screw or a clip on the side of the fill valve assembly. Turning this will raise or lower the float cup, which changes the water shut-off point.
• Ballcock Style: Older toilets might have a float ball on a metal arm. You can usually just gently bend the arm downwards to make the valve shut off a bit sooner.

A malfunctioning fill valve isn't just a nuisance; it's a huge source of water waste. This kind of fault is one of the big reasons behind the growing popularity of water-saving toilets. The UK smart toilet market, valued at around USD 544.7 million in 2024, is expanding as homeowners look for more efficient solutions to prevent problems like a constantly flushing toilet.

If adjusting the float doesn't sort it out, the fill valve itself might be faulty or clogged with grit. Sometimes, a dodgy fill valve can also be the reason your toilet cistern is not filling correctly, which points to a bigger mechanical failure that will likely need a full replacement. By working through these checks, you can be sure you're fixing the right part.

Practical Fixes for the Most Common Toilet Faults

Once you’ve figured out what’s causing your toilet to flush on a loop, the good news is that the fix is usually quite straightforward. With a bit of patience and the right replacement part, you can solve the problem yourself and finally silence that irritating hiss.

This guide will walk you through the most common repairs with clear, actionable instructions. Let's get you kitted out with the practical knowledge to get this sorted with confidence, starting with the most frequent offender: the flapper.

How to Replace a Worn Flapper or Flush Valve Seal

Nine times out of ten, a faulty flapper is the reason your toilet won't stop running. This simple rubber or silicone seal degrades over time, especially in hard water areas, eventually losing its ability to create a watertight barrier at the bottom of the cistern.

To get started, you'll need to turn the water off and make sure the cistern is empty. The flapper itself is usually connected in one of two ways: it either has two "ears" that clip onto posts at the base of the overflow tube, or it simply slides down over the tube.

• Unclip the old flapper: First, gently unhook the lift chain from the flush lever arm inside the cistern. Then, carefully unclip the flapper’s ears from their posts or just slide it off the overflow tube.
• Clean the valve rim: Before you pop the new one on, take a cloth and wipe around the rim of the flush valve opening. Any limescale or grit left behind can stop the new flapper from sealing properly.
• Fit the new flapper: Clip or slide your new flapper into place. Reconnect the chain to the flush lever, leaving just a tiny bit of slack—about one or two links' worth is perfect.

Pro Tip: Take your old, worn-out flapper with you to the DIY shop. UK toilets come in all shapes and sizes, and showing the old part to an assistant is the best way to guarantee you get an exact match and avoid a second, frustrating trip.

Adjusting or Replacing a Faulty Fill Valve

If the flapper looks fine, the next thing to check is the fill valve. This is the mechanism that refills the cistern after you flush. The problem could be as simple as the water level being set too high, or the valve itself might be broken and refusing to shut off.

First, check the water level. It should stop filling about an inch or so below the top of the overflow tube. If it’s too high and spilling over, you’ll need to adjust the float. Most modern UK fill valves have a float cup that moves up and down a shaft. Look for a plastic adjustment screw or a clip you can turn or release to lower the float’s shut-off height.

If adjusting it doesn't solve the problem, the entire valve likely needs replacing. With the water supply turned off, you'll need to unscrew the locking nuts on the outside and inside of the cistern that hold the valve in place. Remove the old valve, making sure you get all the old washers out, and then install the new one by following the manufacturer's instructions. Getting the new washers seated properly is absolutely critical for preventing leaks.

When Simple Fixes Don't Cut It

While most running toilet issues are straightforward, you can occasionally run into a more stubborn problem. If you've replaced the internal parts and the leak is still there, or you've uncovered a more complex issue like a faulty boiler, it might be time to call in a professional. We can help with everything from plumbing faults to expert boiler services. For a closer look at common plumbing headaches around the home, you might find our guide on the top 5 plumbing faults and how to fix them really helpful.

Testing Your Work and Final Checks

After you've finished your repair, it's the moment of truth. Slowly turn the water supply back on using the isolation valve. You'll hear the cistern start to fill.

Keep a close eye on it. Check for any drips around the new fittings, paying special attention to the water supply connection and the nuts securing the fill valve. Once the cistern is full, listen carefully. That constant running water sound should have stopped completely.

Give the toilet a proper flush to make sure everything is working as it should. The flapper should lift correctly, and the cistern should refill to the proper level before shutting off quietly. A successful repair means a silent toilet and your peace of mind restored.

Knowing When It's Time to Call a Professional Plumber

While tackling a constantly flushing toilet is often a rewarding DIY job, there's absolutely no shame in knowing your limits. In fact, being able to spot when a small issue could spiral into a major one is the mark of a smart homeowner.

Sometimes, despite your best efforts, the problem just won't quit. If you've gone to the trouble of replacing the internal parts and your toilet is still running, it’s a strong signal that a more complex issue is at play. That’s a clear sign to get an expert opinion. Likewise, discovering a crack in the porcelain of the cistern or bowl isn't just a minor fault—it's a serious problem that needs immediate professional attention to prevent a catastrophic leak.

When to Put the Tools Down

Certain red flags should tell you the problem is beyond a simple fix. Trying to force a rusted or corroded fitting can all too easily lead to a broken pipe or a sheared bolt, landing you with far more damage and a much bigger bill.

It's probably time to call a plumber if you run into any of these situations:

• Persistent Leaks: You've swapped out the flapper and the fill valve, but that stubborn hiss of running water just won't stop.
• Severe Corrosion: The bolts and fittings are so badly rusted that they won’t budge without extreme force. Don't risk it.
• Complex Systems: You have a concealed cistern (the kind hidden in the wall) or a wall-hung toilet. These are much trickier to get to and repair than standard models.

Water efficiency is a huge concern with a constantly running loo. In commercial buildings, traditional UK toilets can use 6 to 9 litres per flush and account for 70-85% of the building's total water consumption. One London building saved an incredible 1,100 litres every single day just by upgrading its toilets, which shows just how much water a single faulty unit can waste. You can see the full research on the impact of toilet water savings here.

If you’re feeling out of your depth or the repair is getting more complicated than you first thought, don't hesitate. You might also find it useful to learn about other common toilet troubles, so feel free to check out our guide on why your toilet bowl might be leaking.

Our expert plumbers provide fast, reliable toilet repairs to get your home back to normal without the stress. We can also assist with other household jobs, such as specialist washing machine repairs.

Lingering Questions About Leaking Toilets?

Even after you've put the tools down and your repair seems successful, you might still have a few questions about your toilet's quirks. It's completely normal. Here, we tackle some of the most common queries that pop up after fixing a constantly flushing loo, giving you that extra bit of confidence in your handiwork.

How Much Water Does a Constantly Flushing Toilet Really Waste?

You'd be shocked. A toilet that just won't quit can waste a staggering amount of water. Depending on how bad the leak is, you could be looking at anywhere from 200 to 400 litres every single day.

To put that into perspective, a single running toilet can easily double an average person's daily water usage here in the UK. This isn't just an environmental concern; it's a direct hit on your wallet and will show up as a very unwelcome surprise on your next water bill. Fixing it fast is genuinely one of the smartest, most effective water-saving moves you can make at home.

My Toilet Gurgles After Flushing. Is This Related?

It’s easy to assume all strange toilet noises are connected, but this is one case where they’re usually not. While a constantly flushing toilet is almost always an issue inside the cistern, that gurgling sound points to a completely different problem down the line.

Gurgling often signals a partial blockage in your drain pipe or an issue with your plumbing’s vent stack, which is meant to regulate air pressure. If you've managed to fix the running water but the gurgle is still there, the two are likely unrelated. You could try a plunger to see if you can shift a minor blockage, but if the sound sticks around, you may need to investigate a potential drainage issue.

Key Takeaway: A running toilet is a leak inside the cistern. Gurgling is usually a problem with the drain line. Knowing the difference helps you focus your efforts on the right fix.

Can I Use a Universal Repair Kit for My UK Toilet?

Universal repair kits can be a lifesaver, but it’s wise to be cautious. The word "universal" is often a bit optimistic. UK toilets, especially older models or more design-led ones, can have very specific internal parts that don't match the standard fittings.

Your best bet is to always take the old, faulty part with you to the DIY shop. This way, the staff can help you find a perfect match or at least confirm that a specific universal kit will genuinely work for your model. Using a part that looks similar but isn't quite right can lead to a poor seal, which means the leak will continue and you'll be right back where you started.

What Should I Do If My Dual Flush Button Gets Stuck?

A stuck flush button is a classic cause of a running toilet because it holds the flush valve open. The culprit is often a build-up of limescale, push rods under the button that have slipped out of alignment, or rods that are just a fraction too long, stopping the valve from sealing properly.

First, give the button a little jiggle to see if it frees itself. If not, you can usually unscrew the entire button housing from the cistern lid. Carefully lift the lid off and take a look at the mechanism. Check for any grime or blockages and make sure the push rods can move freely. If it still sticks after a good clean and reassembly, a replacement button unit is an inexpensive and straightforward fix.

Sometimes, even with the best of intentions, a plumbing job proves more stubborn than you anticipated. If you've worked through these fixes and are still dealing with a leak, or if you've uncovered a more complex issue, don't hesitate to call in the professionals.

The experts at Go Assist provide reliable and affordable plumbing services, handling everything from a constantly flushing toilet to more complicated repairs. Find out more about our plumbing services and book an expert engineer today.