The 
Ariston Kit B - 3.5 Bar Pressure Reducing Valve
 (part number 406802) is a brass component designed to regulate the cold water inlet pressure for specific Ariston water heaters, ensuring it does not exceed 3.5 bar. It is commonly used with the Ariston Andris and Europrisma ranges. 
Key Details & Specifications
Function: Controls the water pressure to a maximum of 3.5 bar, protecting the water heater and plumbing system from over-pressurization.
Compatibility: Designed for use with Ariston Europrisma EP10, EP15, EP30 (2kW & 3kW) and Ariston Andris Lux 10L, 15L, 30L water heaters.
Material: Made of brass. The exterior finish may be described as bronze.
Dimensions: The product dimensions are listed as approximately 7.5 x 5.7 x 11.5 cm (L x W x H).
Plumbing Size: Features a 15 mm plumbing connection size.
Approvals: The product is UKCA certified and meets BS EN 1074-1, BS EN 12266-1 standards