How often should you check your toilet flapper / fill valve?

A worn flapper silently wastes hundreds of gallons (or litres) and spikes water bills.

A leaking toilet can waste hundreds of litres a day without any visible sign. In metered properties it appears purely as a rising bill that nobody can explain. It is consistently one of the largest sources of household water waste.

1. Do the dye test. Put food colouring or a dye tablet in the cistern and do not flush. If colour appears in the pan within fifteen minutes, the seal is leaking.
2. Turn off the isolation valve and flush. Empty the cistern so you can work in it. There is usually a small valve on the supply pipe just below.
3. Inspect the seal. Feel the rubber. If it is hard, brittle, warped or leaves black residue on your fingers, it has perished.
4. Check the chain or linkage length. Too tight and it holds the seal fractionally open. Too slack and it will not lift properly. Aim for a small amount of slack.
5. Replace the seal or the whole valve. On a modern drop valve, the seal alone is usually replaceable. On older UK siphons, the diaphragm is the equivalent part.
6. Check the fill valve and water level. The level should sit below the overflow. Water running into the overflow means the fill valve needs adjusting or replacing.
7. Restore the supply and retest with dye. Confirm the leak has actually stopped rather than assuming.

• A faint trickle or hissing from the toilet between flushes
• The cistern refilling on its own periodically without anyone flushing, sometimes called phantom flushing
• Visible ripples or movement on the water surface in the pan
• A water bill rising with no change in household usage
• Mineral or limescale staining down the back of the pan

• Assuming a silent toilet is not leaking: many leaks are completely silent and only the dye test finds them
• Using in-cistern bleach blocks, which degrade rubber components and are a common cause of premature seal failure
• Adjusting the water level upward to improve flush performance until it spills into the overflow
• Replacing the flapper but leaving a chain that is too short, which holds the new seal open

• Hard water areas see faster seal degradation from scale
• In-cistern cleaning products significantly shorten component life
• Older toilets with worn seats may need the seat replaced as well as the seal

If the cistern itself is cracked, if the pan is loose on the floor, or if water appears at the base, that is a different problem from a seal and needs a plumber.