Running, Weak-Flushing or Leaking Toilet: Fix Guide
The three toilet failures behind 90% of callouts, and which ones are genuinely DIY.
The endless run
A toilet that runs constantly is losing water over the overflow or past the flush seal. Lift the lid: water climbing towards the overflow tube means the fill valve; water level fine but running anyway means the flapper or drop valve seal. Both parts cost pounds and fit without tools beyond a spanner.
The weak flush
Check the rim jets for scale (a mirror helps), the water level against the marked line, and the flapper opening fully. In hard-water areas the jets scale shut over years, descaling transforms a flush more often than any new part.
Water at the base
A puddle at the base after flushing is the one to take seriously: usually the pan-to-soil seal, occasionally a cracked pan. Rocking the pan even slightly makes it worse. This one is worth a professional, because the failure mode of a DIY reseal is sewage under the floor.
A toilet that will not stop running
Either the fill valve is not shutting off, or the flush valve is leaking back into the pan. Put a little food colouring in the cistern and wait twenty minutes without flushing: colour in the pan means the flush valve. No colour, but the cistern keeps filling, means the fill valve. Both are inexpensive parts.
A wobbly pan
Never ignore it. Movement works the pan connector loose, and the resulting leak goes under the floor where it is found months later by the smell or the ceiling below. Refixing a pan properly, packed and sealed to the floor, not just screwed down harder, is a short job that prevents a substantial one.
Condensation on the cistern
Cold mains water in a warm humid bathroom, not a leak. It drips onto the floor and gets mistaken for one regularly. Better ventilation solves it; so does an insulated cistern liner. Confirm it first by drying everything and checking whether the water reappears without anyone flushing.
Gravity, combi or unvented, the fix is completely different depending on what you have.
Trap, waste, tap base or supply: finding which of the four is actually leaking.
The plumbing details that decide whether a new kitchen works quietly for a decade.
What is actually inside your cistern, and which part to blame for each misbehaviour.