Why does my toilet keep running?

A toilet that keeps running — refilling every few minutes, or never quite silencing after a flush — almost always comes down to one of two parts inside the cistern, and both are straightforward to identify by lifting the lid and watching what happens after a flush.

The flush valve (flapper) is not sealing

If water is slowly trickling from the cistern into the bowl even when nothing has been flushed recently, the valve at the bottom of the cistern that should seal shut is not sitting flush — often because it has warped, or a build-up of limescale is holding it slightly open. You can sometimes hear this as a faint, continuous trickle. It is a cheap part and a short job to replace.

The inlet valve (ballcock) is not shutting off

If the cistern keeps refilling because the water level is not triggering the float to shut the inlet off — often because the float arm has become misaligned, or the valve mechanism itself has worn — water keeps entering and escaping via the overflow, sometimes visible as a pipe dripping outside the property. This is a different part to the flush valve and needs a different fix.

Why it is worth fixing rather than living with

A continuously running toilet can waste several hundred litres of water a day. On a water meter that shows up directly on the bill; even unmetered, it is water being paid for through general rates that is simply going down the drain. It is also almost always a genuinely small job — nobody needs a new toilet to fix a worn flush valve.

When it is bigger than a part

If the cistern itself is cracked, if the toilet rocks at the base, or if this is the third part you have replaced on an old suite in as many years, it may be more sensible to look at a replacement toilet than keep fixing an ageing one piecemeal. Our general plumbing page also covers the wider set of everyday jobs — taps, radiators, running overflows — that come up alongside this one; see general plumbing.