Immediate hot-water supplying system

An immediate hot-water supplying system, comprising:

• a first supply pipe having one end connected to a waterworks and the other end connected to a hot-water tap;
• a return pipe configured to communicate between the one end and the other end of the first supply pipe;
• a plurality of first hot water supply devices, each including a first heating unit which is provided along the first supply pipe and configured to heat water flowing through the first supply pipe, and a circulation pump configured to circulate water in a circulation circuit including the first supply pipe and the return pipe;
• a second supply pipe having one end connected to an upstream side of the plurality of first hot water supply devices of the first supply pipe and the other end connected to a downstream side of the plurality of first hot water supply devices of the first supply pipe;
• a second hot water supply device including a second heating unit which is provided along the second supply pipe and configured to heat water flowing through the second supply pipe, and a second flow amount sensor configured to detect a flow amount of water flowing from the second supply pipe;
• a check valve configured to enable water to flow from the second supply pipe to the second hot water supply device, and disable water to flow from the second hot water supply device to the second supply pipe;
• and
• a controlling unit configured to,
• start to perform a circulation heat keeping operation by starting operation of at least one circulation pump of the plurality of first hot water supply devices for circulating water in the circulation circuit and starting operation of at least one first heating unit of the plurality of first hot water supply devices heating water for flowing through the first supply pipe,
• when the flow amount detected by the second flow amount sensor the circulation heat keeping operation is performed is less than a predetermined hot-water-supply detection flow amount, continue to perform the circulation heat keeping operation by continuing operation of the at least one first heating unit and circulation pump of the plurality of first hot water supply devices, and
• when the flow amount detected by the second flow amount sensor when the circulation heat keeping operation is performed is equal to or more than the hot-water-supply detection flow amount, stop at least operation of the at least one circulation pump of the plurality of first hot water supply devices to stop performing the circulation heat keeping operation and perform a hot-water supply operation by at least one of a first sub-operation and a second sub-operation, wherein:
• the first sub-operation is continuing operation of the first heating unit for heating water flowing through the first supply pipe when the first heating unit is already in operation, and starting operation of the at least one first heating unit of the plurality of first hot water supply devices for heating water flowing through the first supply pipe when the first heating unit is not already in operation;
• and the second sub-operation is starting operation of the second heating unit for heating water flowing through the second supply pipe,
• wherein the circulation pump is configured to circulate water in the circulation circuit including the first supply pipe and the return pipe through only the first hot water supply device, among the first hot water supply device and the second hot water supply device.