Toilet that keeps running: causes and how to fix it

A toilet that runs constantly wastes dozens of litres a day. In most cases it's a simple fault in the cistern you can fix yourself.

Find where it leaks

Almost always the water runs from the cistern into the bowl, not from the pipes. Lift the cistern lid and look: the problem is nearly always one of these three.

1. The float is set wrong

If the water reaches the overflow (the central tube) and runs out there, the float closes too late. Lower the level: there's a screw or a clip on the arm.

2. The bottom seal is worn

If water passes even with the cistern «closed», the round seal under the button (flapper) no longer seals. It pops off and is replaced for a few euros.

3. The flapper is stuck

Sometimes the button mechanism stays half open. Take the unit apart (it usually unscrews by hand) and check the flapper drops freely.

The dye test

To check if the leak is from the seal: put a few drops of food colouring in the cistern. If after 15 minutes the bowl is coloured without flushing, the seal is leaking.