Heating and hot water supply system

A hot water supply system comprising:

• a hot water storage tank;
• a liquid heater configured to heat a liquid;
• a liquid-water heat exchanger configured to exchange heat between the liquid and water;
• a liquid pump configured to pump the liquid;
• a water pump configured to pump the water;
• a water-heating circuit configured to circulate the liquid between the liquid heater and the liquid-water heat exchanger;
• a lower outward path configured to lead the water from a lower part of the hot water storage tank to the liquid-water heat exchanger;
• an upper return path configured to lead the water from the liquid-water heat exchanger to an upper part of the hot water storage tank;
• a middle outward path configured to lead the water from a middle part of the hot water storage tank to the liquid-water heat exchanger via a connection port, the middle part being above the lower part and below the upper part;
• a middle return path configured to lead the water from the liquid-water heat exchanger to the middle part of the hot water storage tank via the connection port;
• a room heater;
• and a controller configured to control a medium-temperature heat accumulating operation configured to accumulate heat in the hot water storage tank by circulating the liquid of the water-heating circuit and making the water flow through the lower outward path and the middle return path;
• and a high-temperature heat accumulating operation configured to accumulate heat in the hot water storage tank by making the water flow through the middle outward path and the upper return path of the water heating circuit, wherein the medium-temperature heat accumulating operation is of a circulation heating type in which the water in the hot water storage tank is circulated a plurality of times to the liquid-water heat exchanger, the high-temperature heat accumulating operation is a once-through heating type in which the water in the hot water storage tank passes through the liquid-water heat exchanger only once, the medium temperature heat accumulating operation increases a volume of medium temperature water at the lower part of the hot water storage tank by heating water from the lower part of the tank and delivering the heated water to the middle part of the hot water storage tank, the high-temperature heat accumulating operation increases a volume of high-temperature water at the upper part of the hot water storage tank by heating water from the middle part of the hot water storage tank and delivering the heated water to the upper part of the hot water storage tank;
• and the medium temperature heat accumulating operation is an operation that does not supply heat to the room heater.