Leaking toilet: where the water is coming from

What to do first

Find the isolation valve on the pipe feeding the cistern. It is usually a small screw with a slot that you turn a quarter turn with a flat screwdriver or a coin. If there is no isolation valve, turn the water off at the stopcock. Mop up, put a towel around the base and check the ceiling of the room below if the toilet is upstairs. Do not keep flushing to see where it leaks, because waste water from the pan is what does the most damage.

Leaks at the base of the toilet

Water spreading from under the pan is the one to take seriously. If it appears after flushing, the likely cause is the pan connector or a cracked pan. If it is there all the time, it may be condensation running down the cistern, or a slow drip from the supply that has tracked down the back. Dry everything, lay a sheet of kitchen roll around the base and watch where it gets wet first.

Silicone around the base can hide a leak for months while water soaks into the floor. Persistent damp at the foot of a toilet can soften boards and stain the ceiling below.

When describing the fault, distinguish water outside the toilet from water running inside the bowl. Note whether the floor was already wet before the toilet was used, and whether the first damp patch sits beneath the cistern or behind the pan. Those observations help separate a supply problem from a waste connection problem without taking the toilet apart. A photograph of the dry area and the place where water first appeared is more useful than a photograph of the whole flooded floor.

Cistern-to-pan leaks

On a close-coupled toilet the cistern sits on the back of the pan with a rubber doughnut washer and two bolts. When that washer perishes or a bolt washer fails, water drips from the joint on every flush. It is usually a repair rather than a replacement, but old bolts are often corroded and ceramic cracks easily if overtightened.

Inlet and flush valve problems

A toilet that keeps running, or trickles water into the pan all day, is losing water internally rather than onto the floor. Either the fill valve is not shutting off, so water rises to the overflow, or the flush valve seal is worn and lets water pass into the pan. Both waste water and can raise metered bills, and both are normally fixed by replacing the valve or its seal.

Pan connector and waste leaks

The pan connector links the toilet outlet to the soil pipe. If it has been knocked, has perished, or the toilet has moved slightly on its fixings, dirty water escapes at the back on every flush. This needs fixing promptly. It is often a case of refitting the pan with a new connector and fixing it down firmly.

Repair or replace

Valves, washers and connectors are worth repairing on a toilet that is otherwise sound. A cracked pan or cistern cannot be repaired reliably and needs replacing. If the toilet is old, stained and has had several repairs, read our guide to toilet replacement cost to see what a change involves.

When a leak has reached the ceiling below

If you can see a stain or drip in the room underneath, stop using the toilet until the source is found. Our guide on what to do about a leak in the ceiling covers making the space safe. We handle the plumbing repair and the ceiling afterwards, and our 24/7 call outs are available when water is coming through.