How To Fix A Dripping (Or Leaking) Toilet Cistern

  • A leaking toilet cistern can be unsightly and sometimes hazardous.
  • Learn how to diagnose and solve your issue with our DIY guide!
man fixing toilet cistern flush mechanism

When your home’s toilet cistern starts leaking, there’s nothing ideal about the situation. Toilet water may be clean, but that doesn’t mean it is any less foul to deal with. No one wants toilet water dripping over their bathroom floor, particularly if they have pets or children running around.

What is a toilet cistern?

A toilet cistern holds the water that is used to flush a toilet after use. There are several variations of the cistern, but they all operate in similar ways, which makes fixing them simpler for plumbers.

You can locate the toilet cistern at the back of the toilet bowl. Many identify this part of the toilet as the toilet “tank” or something similar. There should be a heavy lid that you can lift to see inside the cistern, which will reveal a body of water and a few other odd-looking devices.

Inside of a toilet cistern

Let’s be frank, the inside contents of a toilet tank or cistern look a bit odd. One of the first items you’ll notice will probably be the overflow pipe, which is stationed next to a device that is made up of several components: the float cup, a leak sentry device, and a water level adjustment rod.

There are a few other bits and pieces inside of the tank, including fill and flush valves, and a couple different clips, tubes, clamps, and levers. Most toilet cisterns also have a float of some kind.

Leading down from the cistern, at the back of the toilet bowl, there’s also a shut-off valve.

the inside of a toilet cistern being cleaned with blue cleaning liquid
The inside of a toilet cistern being cleaned with blue cleaning liquid.

Identifying a toilet cistern leak

You’ll know fairly quickly if your toilet has a leak, but not all toilet cistern leaks happen inside the home.

The most noticeable type of leak will be your toilet cistern overflowing or leaking onto your bathroom or washroom floor. These are a common type of toilet cistern leak and quite easy to deal with.

You may also notice that the outdoor overflow pipe is leaking water. It’s unlikely that this kind of leak will draw your attention immediately, but you’ll hopefully notice within a couple of days of the leak starting.

It’s more likely that your toilet cistern leak will happen inside your home because most toilet cisterns are designed to overflow into the bowl of the toilet – which is what is happening when your toilet bowl fills up and the level of water won’t recede.

Ways to spot a leak

A toilet bowl filling to a large capacity shows a rather severe leak. Smaller leaks are harder to notice, but there are some ways you can identify them. The quickest is to place a sheet of dry toilet paper at the back of your toilet pan when your toilet isn’t being used.

If the paper is wet after three hours (or in the morning if you do this overnight), then you have a leak issue to deal with.

Alternatively, during a quiet moment in your home, go into your bathroom and listen for the sound of running or rushing water. This is your toilet still running, even when it hasn’t recently been flushed. Accompanying this, you may notice a trickle of water at the back of the toilet bowl.

What causes toilet cisterns to drip or leak?

For toilet cisterns that have push buttons, leaks are usually caused by a build-up for limescale stopping the mechanism from working correctly. You can attempt to dislodge this build-up by pressing the push button several times in quick succession or holding the button down.

If that doesn’t work, you may need to replace the flush mechanism. This is much cheaper to do than paying a plumber or replacing the toilet system.

Close-coupled toilets also cause leaking issues when they are fitted a certain way. It’s better to fit this variation of toilet at a 90-degree angle or you’ll suffer with plenty of toilet leaks and no one wants that.

Think your toilet cistern is leaking from the bottom of the tank? It might not be. If this area is wet, the water could be condensation, rather than a leak. Check the cistern for cracks, check over the pipes, and do a couple of the leak tests to be sure.

Finally, for leaking overflow pipes, check the float or ballcock of your toilet cistern. When the level that these floats are set at is too high, the level of the water in the toilet cistern will also be too high. This will then cause water to go to the overflow to manage the levels.

In older toilet systems, your overflow pipe will be outside. More modern toilets don’t use an overflow pipe that leads outside, the water goes into the toilet pan, instead.

a toilet system being serviced
Servicing a toilet cistern.

How to fix a leaking toilet cistern

The ease of fixing a leaking toilet cistern will depend on the type of leak your toilet is suffering with.

Arguably, the easiest issue to fix would be a float that is set at the wrong level. You should just need to adjust the float to fix this. In some cases, you may have a broken float that needs to be replaced. To do this effectively, make sure you turn off the water valve and drain the toilet first.

This fix should deal with any trickling or ever-running toilets that continuously leak water after flushing or throughout the day.

The more complex fix

One of the leading causes of leaky cisterns happens when the washers need to be replaced. The washers for your toilet cistern are at the very bottom of the toilet tank.

First, turn off the water valve. Then, take off your cistern’s lid and flush the system. This will drain the water.

You’ll need to undo the nuts under the tank to be able to change the washers. Once you’ve done this, put everything back together and turn the water supply back on. Flush, and hope for success!

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