Toilet running continuously — water constantly trickling

A constantly running toilet is wasting water — typically 200–400 litres per day. UK households can be charged for metered water, so fixing this promptly is both economical and environmentally responsible.

Lift the cistern lid. Watch whether water is overflowing into the pan via the internal overflow tube (a plastic tube inside the cistern sitting higher than the water level) — this indicates the water level is too high. If water is running quietly into the pan without overflow, the flush valve is not seating correctly.

If overflowing: the ball valve is not shutting off the water supply at the right level. Adjust the float height — on a modern Torbeck-type valve, there is a small adjuster screw on the top of the float arm to lower the level. On traditional Portsmouth-type valves, bend the float arm slightly downward to reduce the fill height.

If running quietly through the flush valve: on a siphon-type cistern (older UK systems), the diaphragm washer inside the siphon has split. Pull the siphon up (or unscrew from below), remove the diaphragm, and replace with a new one (£2–£4). This is the most common cause of silent toilet running in pre-2000 UK cisterns.

On modern drop-valve cisterns (Grohe, Ideal Standard, Roca): the rubber sealing flap on the flush valve has worn and is not sealing. Replacement flap valves are typically £5–£15 and push straight on — drain the cistern, remove the old flap from the valve body, fit the new one.

After fixing, add a small drop of food colouring to the cistern water — if colour appears in the pan without flushing, there is still a leak through the flush valve and the repair needs revisiting.