How to Replace a Toilet Flush: Mechanism or Complete Cistern

A leaking toilet flush can waste up to 600 litres a day. Good news: in most cases, replacing the mechanism is simple, quick and inexpensive. Here is how to do it.

Diagnosing the fault

• The flush leaks continuously? The flush valve or the float is at fault
• The button sinks without triggering? The flush mechanism is seized up
• Water runs out of the overflow? The float is badly adjusted or punctured
• The cistern is cracked? The whole cistern must be replaced

The two types of mechanism

There are two main types of toilet flush: dual-flush (two buttons, for a small or large flush) and single-flush. Note the model before buying the replacement, or take the old mechanism with you to the store.

Replacing the internal mechanism

1. Close the water supply valve of the toilet (often a small valve behind the cistern)
2. Flush the toilet to empty the cistern
3. Unscrew the buttons and remove the cistern lid
4. Unclip the old mechanism from the bottom of the cistern
5. Install the new mechanism and screw in the fixing nut
6. Reconnect the chain or the lever to the flush button
7. Turn the water back on and test

Replacing the complete cistern

If the cistern is cracked, unscrew the two bolts holding it onto the pan, remove it, and install the new one repositioning the gaskets. Standard cisterns are easy to find and the installation takes less than an hour.

In the event of a persistent leak after the replacement, check the sealing gaskets between the cistern and the pan: a damaged gasket is the most common cause of residual leaks.