how to change a toilet cistern

How to Change a Toilet Cistern

The toilet is one of the most-used items in a home, and chances are, it’ll need replacing over time - either through wear-and-tear or a change in decor.

However, you don’t always have to change the entire thing - you can always replace parts of a toilet in stages. This may be to save costs or you may have come across an issue. If that’s the case, outside of a flusher or seat, your cistern will often be replaced.

So, Plumbworld is here to explain the entire process involved in replacing and fitting a new toilet cistern. We’ll discuss what a cistern is, what it does and why you may need to replace it over time.

Read to find out how to change a toilet cistern with our easy-to-follow guide…

What is a toilet cistern?

what is a toilet cistern?

The cistern is the upper part of your toilet. If you imagine your toilet in the shape of a letter ‘L’, a cistern is the top, vertical part of this ‘L’.

A cistern, sometimes called a tank, holds the water that’s needed to flush the toilet once it’s been used. Most modern toilets these days have the cistern directly mounted on the toilet bowl - this is called a close coupled toilet. The types of cisterns include:

  • Close Coupled Cistern: As we’ve mentioned, the cistern is connected very close to the pan. 
  • Low-Level Cistern: A style of cistern for traditional toilets. These cisterns are fixed just above the toilet pan and usually have a gap between them and the pan.
  • High-Level Cistern: Another style of cistern for a traditional toilet with a pull lever. These cisterns are fixed high up on your wall above the pan. They will often require a step or step ladder for access.

How does a toilet cistern work?

how does a toilet cistern work?

Toilet cisterns are filled by having water enter the cistern via a supply pipe. The water supply for the system is controlled by a valve. This valve is, in turn, controlled by a plastic float. 

The float monitors the amount of water inside a toilet cistern and it will open or close the valve when it is necessary to fill the cistern and keep the water at the required level. Once the toilet is flushed, the float will recognise there’s no water in the cistern, open the valve, and allow water to enter.

Why should I replace a toilet cistern?

why replace a toilet cistern?

You would only be replacing a cistern for two reasons: style or there’s a fault. A cistern can develop problems for a number of reasons, from large-scale issues to lack of maintenance.

If you notice certain problems with your toilet, such as your toilet keeps running - water constantly running into the bowl - or your toilet won't flush, you may have a cistern issue. The same can be said for a leak, if your cistern keeps filling with water.

A toilet cistern works by pulling water from a tank and sending it into the toilet bowl each time you flush. When a cistern stops working, it or its valves and mechanisms may have become cracked or damaged. The cistern will need to be removed or replaced in order to get your toilet working properly again.

How to replace a toilet cistern

how to replace a toilet cistern

Once you’ve bought a new cistern and unpacked it, you will find all the connections, screws, bolts and installation kit, including a seal. Most cisterns have a way of being fixed to the wall so you will need to check your cistern and measure any gap.

Tip: It’s always best to give the toilet a clean with antibacterial wipes or cleaner before touching it as it’ll make the job a bit more pleasant and remove any harmful bacteria. You can wear safety gloves to keep your hands clean and safe.

Removing your old toilet cistern

Before installing your new toilet cistern, you need to remove your old one. But first, you need to get rid of any water that’s inside. 

Flush the toilet and turn off the water supply, which is done by turning the isolation valve on the water pipe clockwise. Flush the toilet again to remove any excess water, it shouldn’t start to refill. If there is a small amount of water left, soak it up using a towel.

To remove the old cistern, use an adjustable wrench to unscrew the water inlet pipe to disconnect it from the bottom of the cistern. This pipe can still have water in it, so place a towel or shallow tub underneath to catch it and avoid a wet floor, just to be safe.

Then, locate the fixing screws under the cistern and unscrew the nuts to detach the cistern from the toilet bowl. Take care when you do this because water may leak out. Once everything is loose, gently lift the cistern away.

Tip: When you pull everything out, make sure you remove any washers, nuts, bolts and other toilet parts that come with it.

How to fit a toilet cistern

how to fit a toilet cistern

This is a key part of fitting a new toilet, which you can read more about in our dedicated post. At this stage, it is always important to read the manufacturer’s instructions.

Read more: How to Fit a Toilet

Assemble the toilet flush mechanism

Before you get the cistern and pipes, you need to assemble and fit the flushing mechanism - this could be a button or handle. Follow the manufacturer’s instructions, remembering to fit sealing rings where necessary.

Tip: Don’t fit anything too tightly, this may prevent your toilet from flushing properly.

At the same time, assemble any interior parts of the cistern, such as the pump, and fit them in place. It’s much easier to do this now than when the entire toilet is in position as you need to move around it.

Fix the cistern to the toilet pan

Now, it’s time to connect the two core parts of the toilet together. Fit the rubber gasket - if it isn’t attached already - to the flush entrance of the pan. Then, insert the fixing bolts, threading them through the holes in the cistern, using the included rubber and metal washers.

Carefully lift the cistern and position it in place on the pan. The bolts will fit through the holes of the pan while the threaded section of the flushing mechanism will go through the rubber gasket. Then, fit the washers onto the bolts and then secure them. 

Tip: Remember not to fit the washers too tightly - this could damage the toilet over time and become a problem the next time you fit a new loo.

Measure & position the cistern

Check that your cistern is level with a spirit level. If you’ve bought a new cistern that lines up with the fixing holes of your old one, great. Otherwise, mark the wall for fixing holes for the cistern using a pencil.

Your new cistern should come with holes in the back - so you won’t have to drill any in it.

Check for any wires and pipes before drilling the holes into the wall. You can tell whether there are any obstructions through plans or with a detector. If everything is clear, drill the holes in the wall.

Reconnect the water

Reattach the water inlet pipe with your adjustable wrench, but be careful not to have it too tight.

When the pipe is attached and your cistern is fixed in place, switch the water supply back on. Wait for the cistern to fill with water - make sure there are no leaks - and then flush the toilet.

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Don’t forget to check out the rest of our blog for more bathroom advice…How to check your radiators| How to Fit & Replace a Radiator | Essential Heating Tips and Checks for Autumn


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