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Category: Plumbing

A leaking toilet cistern or toilet can waste as much as an astonishing 400 -600 litres of water a day. You could be wasting precious water, causing damage to your home, costing yourself money, wasting valuable eco resources and all without even noticing!

Inside an old style toilet cistern

Inside of a standard toilet cistern

It is likely that if your toilet cistern is leaking onto the floor you will notice it very quickly and deal with it immediately.

If the outdoor overflow is running you will likely notice it within a day or two and fix it quite quickly, however most modern cisterns are designed to overflow into the pan and a slow but steady flow of this type is the type of leak that can cause a waste of water of the type mentioned above.

To help you visualise that, that is equivalent of five bathfulls of water, every day!

Isolating the water is made easier if you have previously fitted isolation valves – this means you can turn off the isolating valves rather than the main stop cock, so that the water is on all over the house except to the cistern that you want to work on.

Find out more about isolation valves and how to fit them in our project here – if you are going to be working on your leaking loo and you haven’t yet fitted service valves, you might as well do it now.

Toilet Cistern Leaking into the pan

If you have a modern push button toilet mechanism where the overflow runs into the pan then the leak is difficult to spot, but you might notice your water bills are getting higher. On closer inspection you may notice that you can hear water running when the toilet hasn’t been flushed or can see a slight but constant trickle at the back of the toilet pan.

Here is some advice on spotting a leak provided by Thames Water:

  1. Wait until 30 minutes after the last flush then wipe the back of the pan dry with toilet tissue.
  2. Place a new, dry sheet of toilet tissue across the back of the pan. Leave it in place for up to three hours without using the toilet (it might be best to do this overnight).
  3. If the paper is wet or torn in the morning, you know you have a leaky loo

If you have discovered a leak the next section tells you how to deal with a cistern that keeps leaking.

Push Button Toilet Cistern Keeps Running

If your push button toilet cistern keeps running it can be caused by a bit of grit or limescale getting into the mechanism. Sometimes this can be dislodged by giving the button a few short sharp taps, or by flushing both buttons and holding them down to ensure the cistern drains fully.

If these methods don’t work it is cheaper and easier to replace the full faulty flush mechanism – see more about repairing and replacing push button toilet cistern fittings here.

Toilet Cistern Leaking onto the Floor

If you have a leak onto the floor and you have a close-coupled toilet the most likely cause is that the cistern and the toilet need to be fitted a precisely 90 degrees – see our project on Close Coupled Toilet leaks here.

If you have water leaking from the cistern and you have a low level toilet then it is likely to be the seal around the pipe where the water comes into the cistern or where it leaves the cistern to flow into the pan. You will be able to tell where the water is coming from by wiping the whole area dry and then using a paper towel to wipe around the joints to see where the water is getting out.

If your toilet only leaks when the toilet is flushed then it is more likely that the leak is coming from the coupling to the waste pipe for the toilet.

Toilet Cistern Leaking From the Bottom

Just check that it is in fact a leak and not condensation. You will be surprised how much water can condense on a cold cistern if the air around it is warm and humid – see more about how to solve this problem in our project about condensation on toilet cisterns.

If it is not condensation and not coming from any of the plumping joints then it could be that you have a cracked cistern, in which case it is much better to replace the cistern.

Dripping Toilet Cistern Overflow

The water level in the cistern is controlled by an adjustable float or ballcock. If the float is set too high then the water level also gets too high, so water runs into the overflow. This can be a pipe that leads outside or, in more modern systems, down into the toilet pan.

Old style standard high level toilet cistern leaking from overflow

You may be able to simply adjust to the float or, if it is broken, you will need to replace it.

There can be several causes of a leaking toilet cistern and if your’s does leak, get it repaired as soon as you can to help save yourself money and also minimise any environmental impact.

There are loads of plumbing project on the site, here is a link to the ones about toilet problems


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