A hot water supply system includes a hot water storage tank configured to store hot water, a plurality of temperature sensors that are installed in the height direction of the water storage tank and that detect temperatures at their installed positions, a main-unit-side hot water supply device that heats hot water in the hot water storage tank, a sub-unit-side hot water supply device, a main-unit-side control board equipped with control means that controls the corresponding hot water supply device, and a sub-unit-side control board. Signals sent from the temperature sensors are input in a distributed manner among the main-unit-side control board and the sub-unit-side control board, and each of the control boards are communicably connected to each other by a transmission line.