22.—(1) Every expansion valve, temperature relief valve or combined temperature and pressure relief valve connected to any fitting or appliance shall close automatically after a discharge of water.
(2) Every expansion valve shall–
(a)be fitted on the supply pipe close to the hot water vessel and without any intervening valves; and
(b)only discharge water when subjected to a water pressure of not less than 0.5 bar (50 kPa) above the pressure to which the hot water vessel is, or is likely to be, subjected in normal operation.