Cistern

A cistern is a tank that holds water above or behind a WC pan ready to be released into the bowl as a flush. UK cisterns must comply with BS EN 14055 and the maximum flush volumes set out in Building Regulations Part G, currently 6 litres for single flush and 4 or 6 litres for dual flush. Internal components typically include a float-operated inlet valve to refill the cistern, an overflow weir and a flush valve operated by a lever, button or pull chain. Older London properties may still have low-level or high-level cisterns connected by a separate flush pipe. Common faults include constantly running fill valves, leaking flush valves and water hammer in the supply pipe. Most issues can be addressed by replacing internal components without disturbing the cistern body.