Cistern not filling

A cistern that fails to refill after flushing usually has a problem with the inlet valve, the float assembly or the cold water supply rather than the drain itself. Worn diaphragms, limescale build-up around the valve seat and misadjusted float levels are the most frequent causes, particularly in hard water areas across Greater London. A partially closed isolation valve beneath the cistern or low mains pressure can also slow or prevent filling. In flats supplied via a header tank, a faulty ball valve or low tank level may be responsible. Building Regulations and BS 6700 set out installation standards for cold water supplies to sanitary fittings. Engineers usually address common causes by descaling or replacing the inlet valve, adjusting the float and confirming adequate supply pressure at the fitting.