Ariston ST 50 ProTech Instructions For Installation, Servicing & Operation page 12

Cold Water
Combination Valve
The cold water combination valve may be fitted in close proximity to the
cylinder, or alternatively, it may be separated to allow the pressure reducing
valve where the mains supply enters the property allowing for balanced cold
water throughout the whole property whilst the 6 bar safety valve is fitted in
close proximity to the cylinder.
A balancing port is supplied on the 22mm and 28mm valves allowing
balanced cold water supply to the rest of the building giving constant results
for mixer and shower valves. If the facility is not needed a plug is supplied.
Refer to Fig. 3.8 and Fig. 3.9
Note!
There should be no other valves fitted between the cylinder and the
EXPANSION valve.