The water circuit module, including plate heat exchanger, water outlet valve and water inlet valve, is the key component for water circuit system control in gas wall-hung boilers. Through the connection with the main heat exchanger, cold water inlet, hot water outlet and external radiators, it can switch between the two water circuits of heating cycle and bathroom heating cycle according to the user's usage condition. The water circuit module also integrates water pressure protection and monitoring of system pressure, flow rate and temperature.