A water heater comprising: a heat exchanger hx having a hx hot water inlet, a hx water return outlet, a hx domestic cold water inlet, and a hx domestic hot water outlet; a controllable three-way proportional valve having a boiler water hot water inlet adapted to accept a boiler water, and to provide a proportionally controllable flow to said hx hot water inlet and a boiler return water outlet, and said boiler return water outlet adapted to return a boiler return water to a boiler; characterized in further comprising a mixing tank mt having a mt cold water inlet adapted to receive a cold water from a source of domestic cold water, a mt hot water inlet, and a mt mixed water outlet, said mixing tank to mix said cold water and a hot water from said mt hot water inlet, and said mixing tank to provide a time delayed mixed water; a constant flow pump fluidly coupled to and disposed between said hx domestic hot water outlet and said mt hot water inlet; a temperature sensor disposed in or on said mixing tank to measure a temperature of said time delayed mixed water to provide a time delayed mixed water temperature; a processor operatively coupled to said temperature sensor and operatively coupled to said controllable three-way proportional valve, said processor to run a feedforward control process based on said temperature of said time delayed mixed water to control a flow of boiler water into said heat exchanger; and wherein said feedforward control process adjusts a proportional operating position of said controllable three-way proportional valve to regulate a temperature of hot water at said hx domestic hot water outlet based on said temperature of said time delayed mixed water temperature. a heat exchanger hx having a hx hot water inlet, a hx water return outlet, a hx domestic cold water inlet, and a hx domestic hot water outlet; a controllable three-way proportional valve having a boiler water hot water inlet adapted to accept a boiler water, and to provide a proportionally controllable flow to said hx hot water inlet and a boiler return water outlet, and said boiler return water outlet adapted to return a boiler return water to a boiler; characterized in further comprising a mixing tank mt having a mt cold water inlet adapted to receive a cold water from a source of domestic cold water, a mt hot water inlet, and a mt mixed water outlet, said mixing tank to mix said cold water and a hot water from said mt hot water inlet, and said mixing tank to provide a time delayed mixed water; a constant flow pump fluidly coupled to and disposed between said hx domestic hot water outlet and said mt hot water inlet; a temperature sensor disposed in or on said mixing tank to measure a temperature of said time delayed mixed water to provide a time delayed mixed water temperature; a processor operatively coupled to said temperature sensor and operatively coupled to said controllable three-way proportional valve, said processor to run a feedforward control process based on said temperature of said time delayed mixed water to control a flow of boiler water into said heat exchanger; and wherein said feedforward control process adjusts a proportional operating position of said controllable three-way proportional valve to regulate a temperature of hot water at said hx domestic hot water outlet based on said temperature of said time delayed mixed water temperature.