Replace a Toilet Flush Valve — Trade Method
Replacing a toilet flush valve is a 30–60 minute job with the right kit and confidence to isolate the water. This is the exact sequence UK plumbers use — including the pressure-test step DIY guides usually skip.
Step-by-step method
1. Isolate the water at the nearest valve or main stopcock
Isolate the water at the nearest valve or main stopcock. Prove zero pressure by opening the outlet.
2. Drain residual water into a bucket
Drain residual water into a bucket. Disconnect the dual-flush valve — usually 15mm or 22mm compression.
3. Remove the old dual-flush valve
Remove the old dual-flush valve. Clean pipe ends with wire wool. Inspect for corrosion or scale.
4. Fit the new dual-flush valve with fresh olives / washers
Fit the new dual-flush valve with fresh olives / washers. PTFE-tape threaded connections 5 wraps clockwise.
5. Hand-tight plus 1 to 1
Hand-tight plus 1 to 1.25 turns with a spanner. Restore water slowly and pressure-test for 15 minutes.
Frequently asked questions
Do I need a plumber to replace a toilet flush valve?+
Not legally — toilet flush valve replacement is not notifiable. But if you cannot confidently isolate the water, get a quote (typically £70–£140).
What size toilet flush valve do I need?+
UK domestic standard is 15mm compression tails. Check your existing fitting first — some older builds use 22mm or imperial 1/2" BSP.
Is the new part guaranteed?+
Reputable brands (Reliance, Pegler, JG Speedfit) offer 5–25 year guarantees on their fittings when installed to instructions.