A leaking toilet cistern is a common problem – here’s how to fix it.

A leaking toilet cistern is a problem that often pops up, but luckily it is fairly to diagnose and remedy. All you need is a few products from your local Builders and these tips.

A toilet cistern is the square water reservoir above the toilet bowl and it’s job is to hold water to be used when the toilet needs to be flushed. The parts of the cistern system are the reservoir itself, an inlet valve that supplies water, a float valve arm that controls the water level, and the outlet valve at the bottom that releases the water to the toilet bowl when the toilet is flushed. Your toilet might have a dual flush universal mechanism; this is a bi-valve that allows you to do a half or full flush, depending on which of the two buttons you press. Each button has a separate release mechanism.

So, if there is a leak from your cistern, it is either from one of these three parts, or you have a cracked toilet. The solutions are really easy.

The first step is to shut off the water supply and flush the toilet to empty the cistern. Once that’s done, use a sponge to remove any remaining water.

When that is done it will be possible to check the inlet valve. Start by removing the ball float by simply unscrewing the fastener. This is made of plastic so you can probably do it by hand, but if it’s too tight, use a plumbing spanner to loosen it and then unscrew it by hand. Pull the split pin out and disassemble the filling mechanism by removing the rubber seals.

At this point, check that the jet sprayer is not clogged – if it is, use a pin to clear out any debris. The rubber O-ring here gets worn over time, which leads to the filling mechanism not shutting off properly. If this happens, water will continue to trickle out. If it looks worn, replace it and insert the jet sprayer followed by the second rubber and re-assemble the inlet valve mechanism. The valves are inexpensive, so it’s good practice to replace them if you disassemble this mechanism, even if they aren’t leaking.

Move on to the water outlet valve. Twist the housing to remove the flushing mechanism and inspect the rubber seal at the bottom. If it is worn or torn it will certainly cause a leak. To replace it, gently pull the new seal over the mechanism and set it in place. Also check that the syphon outlet where the seal sits is clean, as any dirt could cause a leak. When that’s done, replace the outlet valve with a simple turn to the right, then reattach the filling mechanism and the float arm. Turn on the water, wait for the cistern to fill up and then check again for leaks.
If there are no leaks but your toilet is over-filling and the water is running through the overflow and into the bowl, simply bend the arm of the float valve downwards slightly. This will close the inlet valve with the water at a lower level.

If the leak is coming from the main line connected to the sewer, it may well be the wax seal that needs to be replaced. If you want to know how to do that yourself, click here.

And that’s it – so don’t be afraid to tackle those easy plumbing jobs. As always, all the parts and tools are available at your local Builders or online. Get to Builders. Get it done.

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