How to Fix a Running Toilet

A toilet that keeps running after flushing isn’t just annoying — it can waste thousands of litres of water a month. The good news is the cause is usually one of a few common, fixable parts.

Check the flapper valve

The flapper (or flush valve seal) sits at the bottom of the cistern and is meant to seal after flushing. Over time it can warp, crack, or collect mineral deposits that stop it sealing properly, letting water continuously trickle into the bowl. This is the single most common cause of a running toilet.

Check the fill valve and float

If the float is set too high, or the fill valve itself is worn, water keeps entering the tank past the point it should stop, and excess water drains into the overflow tube continuously. Adjusting the float height or replacing the fill valve usually resolves this.

Check the chain length

If the chain connecting the flush handle to the flapper is too short, it can hold the flapper slightly open after flushing. Too long, and it can get caught under the flapper, causing the same problem. A small adjustment often fixes it.

Test for a silent leak

Sometimes a toilet “runs” so quietly you don’t hear it. Add a few drops of food colouring to the tank water and wait 15 minutes without flushing — if colour appears in the bowl, water is leaking past the flapper seal.

When to call a plumber

If you’ve checked the flapper, fill valve, and chain and the toilet still runs, or if any of the internal components look corroded or brittle, it’s worth having it properly assessed rather than repeatedly replacing parts that aren’t the actual cause.