To enhance the heating efficiency of a heating hot water control system with a simple configuration.

In the heating hot water control system, at least a part of the hot water flow is changed to a bypass pipe 9 side by a butterfly valve 10 to adjust the flow rate of hot water through a radiator 6. Thus, even when the hot water flow in the radiator 6 is stopped, a circulating circuit of hot water is constantly formed, and the momentum of hot water can be retained to some degree. As a result, when the butterfly valve 10 is changed again to the radiator 6 side, the radiator 6 can be heated rapidly, and the heating efficiency of the heating hot water control system can be enhanced.