How do I stop a toilet leaking at the base?

Identifying whether it is condensation, the pan connector, the cistern seal or a cracked pan — and which of those you can fix.

Difficulty: intermediate
Time: 1 hr 30 min
Read: 3 min
Safety: caution

Short answer

First establish whether it is clean water or waste, and whether it appears only after flushing. Water only after a flush means the pan connector or the pan-to-cistern seal. Constant moisture with no flush usually means condensation, which is a different problem entirely.

Water at the base of a toilet has four common sources and they need quite different responses. Working out which one you have takes ten minutes of observation and saves either an unnecessary call-out or a serious mistake.

Safety

Water around a toilet base may be waste water. Wear gloves, wash thoroughly afterwards, and disinfect the area. If the leak is from the soil pipe connection rather than the pan seal, it needs a plumber — waste water into a floor void is a health issue and a structural one.

What you'll need

Kitchen paper or dry cloth
Gloves
Adjustable spanner (optional)
Replacement pan connector (optional)

Step by step

Dry the area completely and watch what happens.Dry the floor and the base, then do not flush for an hour. Water reappearing without a flush points to condensation or a supply leak.
Then flush and watch closely.Water appearing only after flushing means the pan connector to the soil pipe, or the seal between cistern and pan.
Check whether it is condensation.Common in warm humid bathrooms with cold incoming water. The whole cistern will be beaded with moisture, not just the base. Ventilation is the fix, not a repair.
Check the supply connection and isolation valve.Follow the pipe up to the cistern. A slow drip there runs down and pools at the base, which looks exactly like a base leak.
Check the doughnut seal between cistern and pan on close-coupled toilets.It perishes over time. Replacing it means removing the cistern, which is straightforward but a two-person job for the lifting.
Check the pan connector at the back.The flexible or rigid connector into the soil pipe. If it has slipped or perished, waste water escapes on every flush and it must be replaced.
Check for a rocking pan.Movement breaks seals repeatedly. The pan should be firmly fixed to the floor; if it moves, that is the underlying cause of everything else.
Look for a hairline crack in the pan.Dry it and dust with talc — a crack shows as a dark line. A cracked pan cannot be repaired and needs replacing.

Tips

Waste water leaking under a floor causes serious damage before it becomes visible. If you suspect the pan connector, do not defer it.
Fixing a rocking pan first is often the whole job — with movement stopped, new seals last instead of failing again in months.
Photograph the existing connector before buying a replacement. There are several types and they are not interchangeable.

Common mistakes

Sealing round the base with silicone to stop it — It traps the leak inside where it damages the floor invisibly. Silicone is finishing, not a repair.
Assuming any water at the base is a base leak — Condensation and a dripping supply connection both pool in the same place and need completely different fixes.
Ignoring a rocking toilet — Movement destroys every seal you fit. The pan must be secure before any repair will last.

Questions people ask

Why is there water around my toilet base only sometimes?

If it appears after flushing, it is the pan connector or the cistern-to-pan seal. If it appears without flushing, particularly in a warm bathroom, it is most likely condensation on the cistern.

Can I seal a leaking toilet base with silicone?

No. Silicone hides the leak while water continues into the floor beneath. Fix the seal or connector causing it; silicone round the base is for finishing only.