A puddle around the base of the toilet almost always points to one of five culprits — and only one of them (a cracked pan) means a full replacement. This guide walks through how to diagnose the cause in five minutes, what you can safely fix yourself, and when to call an emergency plumber in London.
First — is it a leak or just condensation?
In cold weather, water can drip from the outside of a cold cistern onto the pan and pool at the base. Dry the toilet completely, then watch what happens over an hour:
- Water appears only after flushing → failed wax seal or loose closet bolts.
- Water appears constantly, even unused → supply pipe / fill valve leak.
- Water appears after long periods unused, mostly mornings → almost certainly condensation, not a leak.
Cause 1: Failed wax seal (most common)
The wax (or rubber) doughnut seals the pan to the soil pipe in the floor. Over years it dries out, especially if the pan rocks. Water leaks only when you flush. Fix: turn off the supply, drain the pan, unbolt and lift the WC, scrape off old wax, fit a new wax-free rubber doughnut, and re-seat. Typical London plumber price: £90–£140 + parts.
Cause 2: Loose closet bolts
The two bolts that hold the pan to the floor can work loose, letting the pan rock and break the seal. A quarter-turn with a spanner often fixes it — but never overtighten, you will crack the porcelain.
Cause 3: Cracked pan or cistern
Hairline cracks at the base of the pan or around the cistern bolts leak slowly. Dry, then dust with talc to find the crack line. A cracked pan means a full WC replacement — patching it never holds.
Cause 4: Leaking supply pipe or fill valve
Water continuously at the base, even unused, usually traces to the flexi tail under the cistern or the fill valve shank washer. Tighten by a quarter-turn; if it still leaks, isolate the WC and replace the flexi or shank seal — under £15 in parts.
Cause 5: Condensation
In flats with cold mains and warm bathrooms, condensation forms on the outside of the cistern. The fix is improved ventilation, a cistern jacket, or a cold-water mixing valve to lift the cistern feed temperature.
When to call an emergency plumber
Call us if you cannot isolate the supply, water is reaching the room below, or the pan is rocking. Across London our typical attendance is 30–60 minutes, day or night.
Toilet leaking and you cannot stop it? Call 07427 826446 — 30–60 minute response across London, 24/7.