How To Fix A Leaking Toilet Cistern

A leaking toilet cistern is amongst the most common home maintenance problems, mainly due to the fact that a leaking toilet cistern is not always easy to see. A leaking toilet cistern is particularly difficult to notice when it’s happening, but with a little detective work you can identify and fix it.

5 Main causes of a leaking toilet cistern

If you have a leaky toilet cistern, you’re not alone. A lot of people have this problem, and it’s easy to fix. There are a few causes of a leaking toilet cistern:

  1. A problem with the flapper—the rubber part that controls the water level in your bowl. It can wear out over time, or get cracked or broken.
  2. The water valve might not be set correctly—if you’ve recently installed new parts on your toilet or replaced your tank, make sure the water valve is aligned correctly so it doesn’t leak.
  3. The float valve not shutting off—the float valve is what controls how much water fills up your cistern and when it stops filling up (and starts to drain). If this part isn’t working properly, it could cause problems with how much water leaves your cistern while flushing and cause leaks from below as well as above.
  4. An issue with drainage—if there’s a problem with how well your toilet drains, this could cause problems like mold growth in your tank or other issues related to excess moisture inside the tank area itself (such as rusting).
  5. A damaged seal can cause a leaking toilet cistern if the float valve is damaged, or if there’s a blockage in the system, your toilet may be leaking and making more of a mess than it needs to. The main thing to look for when trying to fix a leaky tank is to make sure that water doesn’t get inside, because this could cause rust and other problems as well. 

If you have an older model toilet (pre-1993), there may be an issue with the float valve, which may need replacing or adjusting. You will often see a rubber piece around the float—in order to replace this you’ll need to remove the bottom tank cover plate

Fix a leaking toilet cistern step-by-step 

Leaking toilet cisterns are a common problem, and usually the cause is simply a worn washer in your cistern.

To fix this, you’ll need:

-A screwdriver

-A pair of pliers

-New washers

Step 1: Turn off the tap that sends water to your toilet. Take the lid off your toilet and flush. There should be no water re-entering the bowl.

Step 2: Undo the nuts under your cistern. You may be able to open one with your fingers, but you’ll need multi grip pliers for the other one at the top.

Step 3: Locate the outlet valve (you should see it in the middle of your cistern when you look down). Lift out the valve and remove its washers using a screwdriver, then replace them with new ones.

Step 4: Put the outlet valve back into place and turn on your water supply to your toilet again—letting it refill before flushing–to see if this has solved your problem! If not, it may be time to hire a plumber or buy a new cistern outlet kit and fit it to your toilet yourself. 


Hopefully this article has given you some relief. If you’re nervous about tackling the job yourself, then it definitely may be worth calling a local plumber in to help. We’re based in Hawthorn and our plumbers nearby Richmond, Kew, and Camberwell if you need us urgently.

For more helpful information on toilet maintenance read our post on the best product for unblocking toilets and find out which essential tool you need to keep on hand. You can also take extra measures to keep your toilet clean by using toilet block cleaner. For more posts on other plumbing, drainage, and water related issues visit our blog.

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