Toilet cistern not filling after flushing
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Most likely cause & what to check
Remove the cistern lid and check the water level — it should refill to about 25mm below the overflow pipe within 2–3 minutes.
Check the isolation valve on the water supply pipe to the cistern (usually the pipe going into the base or side of the cistern). The slot on the screw should be inline with the pipe — if it is across the pipe, it is closed. Open it.
Check the float valve (ballcock) — push the float up by hand. If water flows in, the float has sunk or the arm is set too low. Try bending the float arm upward slightly to allow more water in.
If the float is a modern diaphragm fill valve (a cylindrical plastic device) and it has stopped working despite water being present, the diaphragm washer inside has failed — replacement valves cost £8–£20.
Replace the fill valve if adjustment does not resolve it. Shut off the isolation valve, flush to empty the cistern, disconnect the supply and overflow pipes, and fit the new valve following the manufacturer's instructions.
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