Toilet keeps running? What is going on in the cistern

A toilet that keeps running wastes water all day and night, and on a water meter you pay for every drop. The good news is that the cause is nearly always one of three things.

1. The fill valve does not shut off

The fill valve lets water into the cistern after a flush and should stop when the water reaches the right level. If it does not, water rises until it spills into the overflow. On older cisterns that overflow runs outside, so you may see a pipe dripping on the wall. On most newer ones it runs quietly into the pan.

What you can check: lift the lid and look at the water level. If it is up at the overflow pipe or the marked line, the fill valve is the likely culprit. Sometimes it is just set too high and can be adjusted.

2. The flush valve does not seal

Modern cisterns use a flush valve with a seal at the bottom. When that seal wears or gets a bit of debris on it, water trickles constantly into the pan and the cistern keeps topping itself up.

What you can check: look in the pan for a thin ripple running down the back. If it is there and the water level in the cistern is below the overflow, it is the flush valve seal.

3. The button or lever is sticking

A button that does not return fully can hold the flush valve open slightly. Press it a few times and watch whether it springs back.

When it is a plumber’s job

Swapping seals and valves is routine work, but on close coupled toilets it can mean taking the cistern off the pan, and the bolts on older cisterns are often seized. If the cistern is cracked, or the toilet rocks on the floor, it may be time for a new one.

Getting it fixed

Running cisterns, slow fills and flushes that will not hold are everyday jobs for us across Bridgend. Send a photo inside the cistern with the lid off and we can usually tell you what it needs and price it before we start.

Also worth a read: finding a slow leak. Or just send us the job.