# The Water Supply (Water Fittings) Regulations 1999, Paragraph 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.

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Source: https://www.legislation.gov.uk/uksi/1999/1148/schedule/2/paragraph/22 (the official version)
Page: https://openlegislation.uk/water-supply-water-fittings-regulations-1999/schedule-2/paragraph-22
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.