Toilet Cistern Leaking: Into the Pan or Onto the Floor?

A cistern can leak in two quite different ways, and they need different parts. Water that runs into the bowl wastes water quietly and shows on your meter. Water that drips outside the cistern ends up on the floor and, in a flat, in the ceiling below.

Short answer: Into the bowl means the flush valve or siphon seal. Onto the floor means the cistern-to-pan seal, the bolt washers, the inlet connection or the overflow. Close the isolating valve on the supply pipe while you look, and never seal the outside with silicone.

Leaking into the pan

If you hear the cistern refilling on its own, or see a thin ripple running down the back of the bowl, the flush valve is not closing properly. On a push-button cistern the drop valve has a rubber seal at its base that hardens or picks up grit. On a lever cistern, a siphon that leaks is less common but does happen when its joint to the cistern base fails. The food colouring test in the questions below confirms it. Our guide to a toilet making noise when not in use explains the sounds that go with it.

Leaking outside the cistern

• Between the cistern and the pan. The large rubber doughnut seal flattens and cracks over the years. Water appears each time the cistern refills.
• At the bolts. Each bolt passes through the bottom of the cistern with a rubber washer. When a washer fails, a drip forms on the bolt head under the cistern.
• At the inlet. Where the supply pipe connects to the fill valve, a loose nut or perished washer drips steadily, flush or no flush.
• From the overflow. If the fill valve is not shutting off, water rises to the overflow and runs out through it, into the pan or out of a pipe through the wall.

What you can safely do

Close the isolating valve, flush to empty the cistern, and dry everything. A slightly loose inlet nut can be nipped up a quarter turn. Adjusting the float so the water sits below the overflow is also a safe first step. Anything that means taking the cistern off the pan is best left to a plumber, because the old bolts are often seized and the ceramic cracks easily.

Repair or replace

Seals, washers and valves are cheap and nearly always worth replacing. If the cistern is cracked, or your toilet range is discontinued and no matching cistern exists, see replacing a toilet cistern for what that involves.

Need it fixed

Call 07861 933265. There is no call-out charge; repairs are £110 for the first hour and £45 per half hour after, plus parts. If water is also pooling round the foot of the toilet, read toilet leaking from the base too.