Float valve (ballcock)

A float valve is a valve installed in a cistern or storage tank that controls the water level using a floating ball or float mounted on a lever. As the water rises the float lifts the lever, gradually closing the valve until flow stops at the desired level. UK float valves are manufactured to BS 1212 in side-entry, bottom-entry and equilibrium designs and must comply with the Water Supply Fittings Regulations 1999 to prevent backflow into the supply. Worn washers and corroded internal parts are common causes of running cisterns and slowly filling tanks in older London properties. Replacement valves are widely available and usually straightforward to fit. Modern designs include adjustable arms and silent fill cartridges to reduce noise during refilling.