How to Fix a Running Toilet: A Simple Step-by-Step Guide

15th Oct 2026

White bathroom vanity unit with blue tiles

That unmistakable hissing sound coming from the bathroom is the last thing you want to hear, leaving the sound of water trickling away long after you've pulled the flush lever. Having a toilet constantly running is frustrating, and if left ignored, it can quietly rack up your water bill.

As one of the most common bathroom problems, a running toilet is something almost every homeowner will deal with at some point. But before you call out a pricey plumber, there's some good news. Learning how to fix a running toilet is a surprisingly simple task that you can handle yourself.

We'll walk you through easy, step-by-step fixes to get your toilet up and running in no time, featuring expert tips from Brian Toward, CEO here at Wholesale Domestic.

Why is my toilet running?

First things first, it's important to note that, contrary to many people's assumptions, a running toilet isn't caused by a blockage in your pipes. If you're dealing with water that won't drain away, you'll need our guide on how to unblock a toilet instead.

If your toilet keeps running after flushing without the handle or button being pressed again, the problem almost always lies inside the cistern. Typically, it comes down to one of two main culprits: a float valve that's sitting too high, or a worn-out flapper that needs to be replaced.

If the float valve is the issue, it's probably set so high that the top of the water isn't pushing it upwards, stopping the toilet from refilling. This can usually be fixed with a simple adjustment, but sometimes requires a full fill valve replacement.

If the flapper's the issue, it's likely worn down so much that it no longer forms a tight seal in your cistern, which can also cause the bowl to keep refilling.

How to adjust toilet float to stop running

Your toilet float is a small, buoyant device inside the cistern that rises with the water level. Once it reaches a certain height, it triggers the fill valve to shut off the water supply. If this is set incorrectly, it's the most common reason behind a running toilet.

Thankfully, adjusting the float is also the easiest and quickest fix. Here are five simple steps to get it sorted:

1. Remove the cistern lid

The first step is to gain access to the inner workings of your toilet. For a regular close-coupled model, lift the ceramic lid off the top of the cistern and carefully set it aside on a soft towel to prevent chipping.

If you have a wall-mounted toilet with a concealed cistern inside the wall, you'll need to remove the flush plate. This usually involves pushing the plate slightly upwards and pulling it forward to unclip it, giving you access to the mechanism behind the wall.

2. Locate the fill valve

Once you're inside, you need to identify the right part.

You'll usually find the fill valve sitting on either the left or right side of your cistern, depending on where your water supply comes in. It looks a bit like a plastic tower. Attached to this tower, you'll see the float.

On older toilets, this might be a large plastic ball on the end of a metal arm, but modern toilets usually have a small plastic cup that slides up and down the main fill valve shaft.

3. Rotate the adjuster to raise the float

Next, you need to adjust the float so it stops the water flow before it spills into the overflow tube.

To adjust a modern float, look for a long plastic screw or a dial attached to the float mechanism. Turning this adjuster will raise or lower the float. You'll want to adjust it so the water level stops about one inch below the top of the open overflow tube.

If you've got an older ball float, you can sometimes just gently bend the metal arm downwards to achieve the same result.

4. Test the flush

With the float adjusted, give the toilet a flush. Watch the water drain out and the cistern refill. The water should rise, push the float up, and shut off completely about an inch below the overflow tube without any continuous hissing. If it doesn't, your issue is likely being caused by something else.

5. Replace the lid

If the water stops right where it should and the running sound disappears, your job is done. Carefully place the ceramic lid back onto the cistern or close up your wall access hatch.

My toilet won’t stop running even when the float is up

Sometimes, the simplest fix doesn't quite do the trick. If you've tried adjusting the float to the correct height and your toilet keeps running after you flush, you're likely looking at a different mechanical failure. This usually points to a problem with the flapper or the fill valve itself.

How to tell if your flapper needs to be replaced

The flapper is the rubber seal at the bottom of the tank that lifts when you flush. To check whether it's failing, turn off the water supply and inspect the flapper closely. If it looks warped, cracked, or feels hard and brittle rather than soft and flexible, it's no longer creating a tight seal.

Another clear sign is to put a few drops of food colouring into the cistern and see if the colour slowly seeps into the toilet bowl without flushing.

How to tell if your fill valve needs to be replaced

If the flapper is in good condition and holding water, the fill valve is likely at fault.

Signs of a broken fill valve include:

Water continuously spraying from the top of the valve
A loud squealing or hissing noise that never quite goes away
A float mechanism that's stuck and won't move up and down the shaft

What you’ll need to fix a running toilet

If you need to replace the flapper or the fill valve, you'll need to gather a few basic tools before you get started:

A new flapper (if replacing)
Wire cutters
Flathead screwdriver
Measuring tape
Bucket
New fill valve (if replacing)

How to replace a toilet flapper

If you're wondering how to fix a toilet that keeps running due to a faulty seal, replacing the flapper is the answer. While it's slightly more involved than turning a screw on the float, it's still a simple task that you can complete without calling a professional.

Here are five easy steps:

1. Turn off your water supply

Before you unclip anything, you'll need to shut off the water to prevent a flood in your bathroom.

"Look for the isolation valve on the water pipe located just behind or below the toilet," Brian advises. "It usually looks like a small metal screw head. Use a flathead screwdriver to turn it a quarter turn until it sits horizontally across the pipe. If you don't turn this off, the cistern will just keep trying to refill the entire time you're working, making a huge mess."

2. Measure the old flapper chain

Once the water's off, flush the toilet to empty the tank. Before removing the old flapper, take your measuring tape and check the length of the chain connecting it to the flush handle. Jot the length down so you have a reference for the length needed for your replacement flapper. This helps make sure it forms a solid seal when at rest.

3. Remove the old flapper

Now you can take the faulty part out of the cistern.

"Taking the old flapper out is usually very easy," says Brian. "First, unclip the chain from the long arm of the flush lever. Then, reach down to the bottom of the cistern. The flapper is generally hooked onto two small pegs on either side of the overflow tube. Slide the rubber ears off those pegs, and you can lift the whole piece right out."

4. Install the new flapper

With the old flapper out of the way, it's time to install the fresh one.

Place the new flapper into the cistern, slotting the rubber ears onto those same two pegs at the bottom of the overflow tube.

If your new chain is significantly longer than the old one, grab your wire cutters to snip off the excess length.

Next, clip the chain into the flush lever mechanism. If the chain's too long, it won't hold the flapper up when the lever's down, and it might get caught under the seal. If you've got a modern push-button flush, the setup might look a little different, but there'll always be a designated clip or hook for the chain.

5. Test the flush

Finally, turn the water isolation valve back on (turning the screw so it sits vertically in line with the pipe) and let the cistern fill. Flush the toilet a few times to check the new flapper lifts smoothly and drops down to form a solid, leak-free seal.

How to replace a toilet fill valve

If the flapper is fine but the water won't stop pumping, you'll need to replace the fill valve. While this is the most complex of the three methods, with some patience, it's still a relatively easy process.

1. Turn off the water supply

Just like the flapper replacement, start by turning off the water supply at the isolation valve next to the toilet. Then, flush the toilet to empty as much water as possible from the cistern.

2. Remove the old fill valve

With the tank empty, you can safely remove the broken valve.

"Unscrew the mounting nut under the cistern that holds the fill valve in place with your hand," Brian advises. "It's a good idea to place a bucket under this area, as water may drip out when removed.”

“Pull the old valve up and out, then clean the spot around where the fill valve was removed so there's no limescale or debris that could affect the performance of the new one."

3. Adjust your new valve

Before installing the new fill valve, you'll need to adjust its height to fit your specific cistern.

"You don't want the new valve sitting too high or low," Brian says. "Adjust the height of the fill valve so the top of the plastic cap sits about three inches above the top of the overflow tube. You might also need to adjust the float valve height by turning the adjuster. This should sit roughly one inch below the top of the overflow tube."

4. Fix it into position

Once it's the right height, you can secure it into the tank.

Before fitting the new fill valve, make sure the rubber gasket is present on the bottom. Place it into its slot in the cistern and secure it in place by tightening the nut underneath the tank by hand. Never use a spanner to tighten this plastic nut, as you can easily crack the ceramic tank.

5. Connect any tubes (if needed)

Many modern fill valves come with a small rubber tube that directs water into the overflow to refill the toilet bowl.

Brian says, "If your new fill valve has a rubber tube, it'll also come with a clip that needs to be secured onto the overflow tube. Once you've done that, slot one end of the rubber tube onto the port on the side of the fill valve, and the other end onto the clip you just placed on the overflow tube. This makes sure water goes exactly where it needs to."

6. Reconnect your water supply

Finally, reconnect the water supply pipe to the bottom of the fill valve. Turn the isolation valve back on and watch the tank fill. Check the bottom of the cistern for any drips, test the flush, and enjoy the sound of a quiet bathroom!

Frequently asked questions

What is ‘ghost flushing’?

Ghost flushing is the term used for when your toilet sounds like it's flushing itself without anyone touching the handle.

While it might sound spooky, this happens when water slowly leaks out of the cistern and into the bowl, usually because of a faulty flapper. Once the water level in the cistern drops low enough, the fill valve automatically kicks on to top it back up, creating that sudden rushing water sound.

Can a running toilet cause damage?

In most cases, a running toilet won't cause any structural damage to your home, but it can cause secondary issues. Continuous running water can create excessive condensation on the outside of your cistern in colder months.

This moisture can drip down onto your flooring, leading to dampness, mould, or damage to your floorboards over time. If the overflow tube also fails, the continuous water flow could eventually spill out of the tank and flood your bathroom.

How much water does a running toilet waste?

A running toilet is incredibly wasteful and can severely impact your water bills. A leaking toilet can waste between 215 and 400 litres of potable (drinkable) water every single day.

You can learn more about how small leaks impact our environment in our guide to UK water waste.

How long does it take to fix a running toilet?

Fixing a running toilet is a quick job. Adjusting the float takes less than five minutes. If you need to replace the flapper or the fill valve, it generally shouldn't take you longer than 30 minutes, provided you follow the method above and have the right tools on hand.

Upgrade your toilet setup today at Wholesale Domestic

While replacing a flapper or fill valve is a great DIY skill to have, sometimes an older toilet is just past its prime. If you're regularly finding that the float needs to be adjusted, or you're dealing with a running toilet after replacing the fill valve, it might be time for an upgrade.

At Wholesale Domestic, we offer a huge range of high-quality toilets designed with modern, reliable flush mechanisms. Whether you're looking for a classic close-coupled toilet for easy maintenance, a sleek wall-hung model to save floor space, or a minimalist back-to-wall design for a contemporary finish, we've got just what you need to complete your bathroom.

Shop the collection today, or see our blog for more helpful how-to guides and bathroom inspiration.

Contents: