The water circuit module, which includes the plate heat exchanger, outlet valve and inlet valve, is the key component for water circuit system control in gas wall-hung furnaces. Through the connection with the main heat exchanger, cold water inlet, hot water outlet and external radiator, the heating heating cycle and bathroom heating cycle are switched between the two circulating water circuits according to the user's usage. The water circuit module also integrates water pressure protection and monitoring of system pressure, flow and temperature.