Technical Booklet P Sanitary Appliances Unvented Hot Water Storage and Scalding·Page 14·2.12
Check valve and expansion vessel
Unvented hot water storage systems must include a check valve complying with BS EN 13959 to prevent water expansion into the cold supply, and an expansion vessel complying with BS 6144 sized to accommodate all water expansion on heating.
An unvented hot water storage system should also have –
(a) a check valve complying with BS EN 13959 to prevent the expansion of water to the cold supply; and
(b) an expansion vessel complying with BS 6144 sized to accommodate all the expansion of the water on heating.
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