Technical Booklet P Sanitary Appliances Unvented Hot Water Storage and Scalding·Page 13·2.9
Temperature Safety Devices
Unvented hot water storage systems must have a non-self-resetting thermal cut-out on each heating source and one or more temperature relief valves to limit stored water temperature, factory fitted and operating in sequence as temperature rises.
An unvented hot water storage system should have the following safety devices to limit the temperature of the stored water –
(a) a non self-resetting thermal cut-out on each heating source, complying with either –
(i) BS EN 60335-2-73+ A2; or
(ii) BS EN 257, when the stored water is heated by a gas burning appliance; and
(b) one or more temperature relief valves to BS 6283 Part 2 or BS EN 1490 which have a total discharge capacity (measured in accordance with Appendix F of BS 6283: Part 2 or BS EN 1490) at least equal to the power input to the water.
These safety devices should be factory fitted and located directly on the storage vessel, operate in sequence as the temperature rises and be additional to any thermostatic device fitted to control the temperature of the stored water.
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