Toilet Won't Stop Running? Here's What's Actually Wrong

A leaking loo is the quietest expensive fault in the house. A continuously passing flush valve can waste 200 to 400 litres a day — more than a family of four uses. On a water meter, that's a bill shock; in a flat, it's often the first sign of a problem the neighbour downstairs finds before you do.

Here's the quick diagnosis we run on every toilet repair call across Barnet.

Dry the back of the pan above the water line and stick a square of toilet paper to it. Come back in ten minutes. Wet paper means water is trickling from the cistern into the pan — a flush valve or diaphragm seal problem.

On modern dual-flush cisterns the drop valve seal is a soft washer that hardens with limescale — the number one fault in North London's hard water. The seal is inexpensive, but the cistern must be drained and the valve lifted out, which is fiddly on close-coupled and concealed units.

If water is running into the overflow, the fill valve isn't shutting off or the float is set too high. Sometimes it's just a debris fragment in the valve seat after mains work in the street; often the valve is scaled and needs replacing.

Dual-flush push buttons stick partly depressed, holding the valve open. If your toilet only runs after certain flushes, that's usually the button rod or the frame, not the valve.

If you have a concealed cistern behind tiling — increasingly common in the bathroom installations we do — repairs are done through the flush plate aperture. Get someone who has done it before; forcing a scaled valve out of a boxed frame is how tiles crack.

If you let property in EN4, EN5 or N12, a running toilet in a tenanted flat can quietly run for months. A twice-yearly plumbing maintenance visit across a portfolio usually pays for itself on water bills alone.