How to Fix a Running Toilet

A running toilet, where water keeps flowing into the cistern after the flush has finished, is one of the most common household plumbing issues. It's usually caused by one of a few simple parts, and it can quietly waste a surprising amount of water if left unchecked.

Check the flush valve (flapper)

The most common culprit is the flapper or flush valve at the bottom of the cistern. If it's worn, warped or not sealing properly, water leaks from the cistern into the bowl, so the cistern never stops refilling. Replacing the flapper is usually a cheap, straightforward fix.

Check the fill valve and float

If water keeps flowing into the cistern even after it's full, the fill valve may not be shutting off. This is often because the float, which rises with the water level to close the valve, is set too high or is sticking. Adjusting the float level down, or replacing a faulty fill valve, usually resolves it.

Check the flush button or handle and chain

If the flush button sticks, or the chain connecting the flush lever to the flapper is too short or tangled, the flapper can be held open and allow a continuous trickle. A chain that's too long can also get caught under the flapper and stop it sealing.

Check the overflow tube

If the water level in the cistern is set too high, water continuously flows into the overflow tube and down into the bowl. Lowering the float so the water stops just below the top of the overflow tube fixes this.

When to call a plumber

If the cistern is concealed inside the wall or toilet unit, or the problem persists after checking the flapper and float, it's worth calling a plumber. Some modern dual-flush mechanisms and concealed cisterns are fiddly to access and easy to damage, so professional help can be cheaper than a botched DIY repair.