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To protect the appliance and to prevent excessive flow rates, a pressure reducing valve must be fitted to limit the maximum supply pressure to 3 bar.
Whenever a pressure reducing valve or other device containing a non-return valve is fitted to the mains water supply entering the boiler, a mini expansion vessel must be fitted after the device in order to protect the appliance from the expansion due to heating of the water in the domestic hot water pipe work.
Note that the flow rate from individual taps is dependent on the number of outlets being operated together, as well as the length and size of pipe work and the mains supply pressure.