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HOW TO: Replace a float valve and ballcock 🚽

Updated: Jun 24

Do it yourself in just 7 easy steps

When it comes to household tasks, there's a certain feeling of empowerment in being able to tackle simple plumbing issues yourself.

One task that might pop up from time to time is the replacement of a float valve and ballcock in your toilet's tank.

Before you find yourself knee-deep in water, let's dive into the ins and outs to get the job done properly.

Understanding the components

Let's start by breaking down the key players.

The float valve, often referred to as the fill valve, is the unsung hero responsible for regulating the water flow into your toilet's tank. Think of it as the gatekeeper that ensures your tank doesn't overflow or run dry.

Now, onto the ballcock. This is the component that keeps your tank's water level in check. It's the one with the float ball attached to it. Traditional ballcocks are those old-school mechanisms we've all encountered, but modern times have introduced sleeker fill valves that do the same job with a touch more finesse.

Tools & Materials

Before diving headfirst into some DIY plumbing, you'll need to arm yourself with the right tools and materials.

Grab your adjustable spanner, screwdriver set, and pliers.

You'll also need a replacement float valve assembly, a new ballcock assembly, and some PTFE tape to ensure leak-free connections.


Step-by-Step Replacement Guide

Water supply valve

Step 1: Turn off the water supply

First things first, let's isolate the water supply to your cistern or header tank. No one wants an impromptu indoor pool, after all.

There may be an isolation valve right next to your float valve - if so, turn it to the off position.

If not, then find your mains stop tap (normally in the back of a kitchen cupboard, in the bathroom or under the stairs) and turn it off.

Step 2: Empty the tank and disconnect the supply line

Flush your toilet to empty the tank.

Then, place your adjustable spanner on the compression nut on the end of the valve, and grip the body of the valve with your pliers.

Turn the spanner, loosen the compression nut, and once undone, pull the supply pipe out of the end of the valve.

Step 3: Remove the old valve

One the water supply pipe is disconnected, use your adjustable spanner to hold the body of the valve with your pliers while you undo it.

Once undone, remove the old valve a chuck it in the bin.

Step 4: Insert replacement valve

Screw the replacement float valve in with with your fingers, then tighten with an adjustable spanner, holding the body of the valve in place with your pliers.

Applying PTFE tape to valve thread

Step 5: Reconnect the water supply line

Push the water supply pipe back into the body of your new float valve, until it hits the end.

Once it's in place, wrap some PTFE tape around the thread of the valve, then tighten the compression nut wth your adjustable spanner.

TOP TIP: Don't overtighten! This can cause leaks.

Step 6: Attach the new ballcock

We're nearly at the finish line!

Take your new ballcock, and screw it onto the end of the valve you just fitted.

Step 7: Time to test

Once you're confident that everything is connected securely, turn the water isolation valve, or mains stop tap, back on

Quickly make your way back to the cistern to check for any leaks. If there are, tighten the compression nuts until the leaks stop.



  • You may find that due to slight differences in the float valve arms (different length or bend) that the volume of water in the cistern is different to before.

  • If you find that the water level is too high, to the point where it might overflow and leak, or even the opposite where it's not filling enough, the valve will need adjusting to allow less or more water to flow.

  • To increase water levels, bend the arm slightly upwards.

  • To decrease water levels, bend the arm slightly downwards.

  • Watch the water level to make sure it stops before the overflow, otherwise you'll waste water and potentially increase your water bills!

Visit any of our branches to find the tools and materials you need to carry out any DIY task. We're also happy to help with any advice you need.


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