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Leaking Toilet Cistern: Main Causes And How To Fix It

Blocked basin NLK-Plumbing Brisbane

Have you ever come home to find your bathroom floor flooded with water from a leaky toilet cistern? If so, you’re not alone. Toilet cistern leaks are very common and can cause a lot of damage. In this blog post, we’ll discuss the main causes of leaking toilet cisterns and how to fix them. Stay dry!

What is a cistern and why is it used?

A cistern is a watertight container that is used to store rainwater. Cisterns are often found in the underground water supply line, and they can be made from a variety of materials, including concrete, stone, and plastic.

One of the main benefits of using a cistern is that it helps to conserve water. In many areas of the world, freshwater resources are limited, and cisterns can help to reduce the amount of water that is used for household tasks such as laundry and watering plants.

In addition, cisterns can be used to provide an emergency water supply in case of a power outage or natural disaster. While cisterns vary in size and design, they all serve the same basic purpose: to collect and store rainwater.

 How to identify whether you have a leaking cistern tank

A leaking cistern tank can be a frustrating problem. Not only does it waste water, but it can also cause significant damage to your home.

Fortunately, there are a few tell-tale signs that can help you identify whether you have a leaking cistern tank.

One of the most obvious signs is water pooled around the base of the tank. Another is a sudden decrease in water pressure, which can be caused by a loss of water in the tank.

If you suspect that your cistern tank is leaking, it’s important to act quickly. The sooner you address the problem, the less damage the water leaks will cause.

toilet leak

The most common causes of leaking toilet cisterns

Toilet cisterns are prone to leaking for a number of reasons. Leaking toilet cisterns are caused by faulty washers, worn-out flush valves, or a misaligned water supply valve. If you have a leaky toilet tank, you’ll need to identify the source of the leak and then take the appropriate steps to fix it to save the remaining water.

Worn-out washers

If you have a leaking toilet tank, the first thing you should do is check the condition of the washers. Washers are small rubber or plastic discs that create a seal between the flush valve and the water supply valve.

Over time, these washers can become worn out or damaged, which can cause them to leak. To replace a worn-out washer, simply remove the old one and install a new one in its place. However, you can also install a spud washer to avoid the excess water to leak.

Damaged flush valve

Another common cause of leaks is a damaged or worn-out flush valve. The flush valve is the part of the toilet that allows water to enter the toilet bowl when you flush the toilet.

Over time, the rubber or plastic components of the flush valve can become worn out, which can cause it to leak. If your flush valve is leaking, you’ll need to replace it with a new one.

A faulty fill valve

One of the most common causes of a leaking cistern is a faulty fill valve. The fill valve is responsible for controlling the flow of water into the cistern, so if it’s not working properly, it can cause water to leak. fortunately, replacing a fill valve is usually a fairly straightforward job that anyone can do with just an adjustable wrench.

Misaligned water supply valve

The third most common cause of leaky toilets is a misaligned water supply valve. The water supply valve is located at the back of the toilet tank and is responsible for supplying water to the tank.

If the water supply valve is not properly aligned, a water leak occurs. To fix this problem, simply shutoff valve and readjust the water valve so that it is properly aligned.

Faulty flush lever

Another common cause of cistern leaks is a faulty flush lever. The flush lever is what you use to activate the flushing mechanism, so if it’s not working properly, water can leak out when you try to flush the toilet.

If you’re not sure what is causing your toilet tank to leak, you can always call a plumber for help. A professional plumber will be able to quickly identify the source of the leak and make the necessary repairs.

How to fix a leaking toilet cistern yourself

Leaking toilet cisterns can be a real nuisance. Not only do they waste water, but they can also cause your water bill to skyrocket.

Fortunately, there are a few simple steps that you can take to fix a leaking toilet cistern yourself. The first thing that you need to do is identify the source of the leak.

If the leak is coming from the fill valve, simply replace the washer and/or O-ring. If the leak is coming from the flush valve, you may need to replace the entire valve as soon as possible to stop wasting water.

Once you have replaced the faulty parts, it is important to test your repair job by using the flush handle to flush the toilet several times.

With a little patience and some basic plumbing skills, fixing a leaking toilet cistern is a relatively straightforward task that anyone can do.

What to do if the problem persists

If your toilet cistern is still leaking after you’ve tried the above solutions, it’s time to call a professional.

A plumber will be able to determine the root cause of the problem and fix it quickly and efficiently. In the meantime, continue to monitor your toilet cistern closely to ensure that no further water damage is done.

How to prevent your toilet cistern from leaking in the first place

The first step in preventing your toilet cistern from leaking is to have it installed by a professional. They will know how to properly seal the cistern and connections to prevent leaks and drain water.

If you notice any water around the base of your toilet and an overflow tube, it is important to investigate the cause right away. A small leak can quickly turn into a big problem if left unchecked.


Toilet cisterns can leak for a variety of reasons, but the most common cause is a faulty valve. If you have a leaking toilet cistern, it’s important to identify the cause and take steps to fix it as soon as possible. By doing so, you can prevent further water damage and save money on your water bill.

If you’re not sure how to fix a leaking toilet cistern, it’s best to call a professional plumber. However, if you’re handy and have some basic plumbing knowledge, you may be able to fix the problem yourself. Either way, it’s important to take action as soon as you notice a leak.

Check out here how to unblock sewage drain.


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