Technical Booklet P Sanitary Appliances Unvented Hot Water Storage and Scalding·Page 7·88(1)-(2)
Unvented hot water storage systems - safety devices
Unvented hot water storage systems over 15 litres capacity must incorporate safety devices to limit stored water temperature to 100°C maximum and devices to control and relieve excessive pressure.
This regulation shall apply to any hot water storage system (other than a system or part of a system used solely for space heating or an industrial process) that has a storage vessel which— (a) has a capacity greater than 15 litres; and (b) does not incorporate a vent pipe to the atmosphere. A hot water storage system to which this regulation applies, whether heated directly or indirectly, shall incorporate— (a) safety devices to ensure that the temperature of the stored water does not exceed 100°C at any time; and (b) devices to control the working pressure and to relieve excessive pressure.
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