The water circuit module, comprising a plate heat exchanger, outlet valve, and inlet valve, is a critical component for controlling the water circuit system in gas-fired wall-mounted boilers. By connecting to the primary heat exchanger, cold water inlet, hot water outlet, and external radiator, it switches between the heating circulation loop and the domestic hot water circulation loop according to user demand. The module also integrates functions for water pressure protection and monitoring of system pressure, flow rate, and temperature.