How to Fix a Running Toilet (UK)
Diagnose and fix a UK toilet that won't stop refilling. Fill valve, flush valve, seal or float — root cause guide.
FluidmasterGeberitRocaWirquin
Test which side is failing
Dye test: food colouring in the cistern. If it appears in the pan without flushing = flush valve seal. If water audibly refills but pan stays clean = fill valve overshoot.
Fixes
- Flush valve seal — replace the doughnut seal (£3).
- Fill valve overshoot — adjust float or replace valve.
- Cracked overflow — replace whole flush valve assembly.
- Debris on seat — clean and re-seat.
Frequently asked questions
- Why does the toilet run only every 30 min?
- Cistern leak past flush seal is refilling slowly — fill valve then kicks in. Replace the flush valve seal.
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