A hot-water supply system comprising: a heat source; a primary circulation circuit communicating with the heat source; a heat storage tank configured to store hot water; a secondary circulation circuit communicating with the heat storage tank; a circulation circuit heat exchanger configured to heat hot water circulating in the secondary circulation circuit, through a heat medium circulating in the primary circulation circuit; a controller, a notification unit; a first temperature detection unit provided in the primary circulation circuit between an inlet of the circulation circuit heat exchanger and the heat source; and a second temperature detection unit provided in the secondary circulation circuit between an outlet of the circulation circuit heat exchanger and the heat storage tank, the primary circulation circuit including a first pump configured to circulate the heat medium, a first flow control device configured to control a circulation amount of the heat medium, and a first flow rate sensor configured to detect a flow rate of the circulating heat medium, the secondary circulation circuit including a second pump configured to circulate the hot water, a second flow control device configured to control a circulation amount of the hot water, and a second flow rate sensor configured to detect a flow rate of the circulating hot water, the controller being configured to control the first flow control device and the second flow control device so that the flow rate of the heat medium circulating in the primary circulation circuit and the flow rate of the hot water circulating in the secondary circulation circuit are equalized, wherein, the controller is configured to, in a heat storage operation, use a flow rate of the heat medium circulating in the primary circulation circuit as a target flow rate of the hot water circulating in the secondary circulation circuit, wherein, the controller is configured to, in a test operation, obtain a temperature difference between a first temperature detected by the first temperature detection unit and a second temperature detected by the second temperature detection unit when the first temperature and the second temperature are in a predetermined reference range, the controller is configured to, in a heat storage operation, obtain a temperature difference between the first temperature and the second temperature when the first temperature and the second temperature are in the reference range, and the notification unit is configured to, when a difference between the temperature difference obtained at the test operation and the temperature difference obtained at the heat storage operation is equal to or more than the predetermined reference value, notify that a time for performing maintenance of the circulation circuit heat exchanger comes. a heat source; a primary circulation circuit communicating with the heat source; a heat storage tank configured to store hot water; a secondary circulation circuit communicating with the heat storage tank; a circulation circuit heat exchanger configured to heat hot water circulating in the secondary circulation circuit, through a heat medium circulating in the primary circulation circuit; a controller, a notification unit; a first temperature detection unit provided in the primary circulation circuit between an inlet of the circulation circuit heat exchanger and the heat source; and a second temperature detection unit provided in the secondary circulation circuit between an outlet of the circulation circuit heat exchanger and the heat storage tank, the primary circulation circuit including a first pump configured to circulate the heat medium, a first flow control device configured to control a circulation amount of the heat medium, and a first flow rate sensor configured to detect a flow rate of the circulating heat medium, the secondary circulation circuit including a second pump configured to circulate the hot water, a second flow control device configured to control a circulation amount of the hot water, and a second flow rate sensor configured to detect a flow rate of the circulating hot water, the controller being configured to control the first flow control device and the second flow control device so that the flow rate of the heat medium circulating in the primary circulation circuit and the flow rate of the hot water circulating in the secondary circulation circuit are equalized, wherein, the controller is configured to, in a heat storage operation, use a flow rate of the heat medium circulating in the primary circulation circuit as a target flow rate of the hot water circulating in the secondary circulation circuit, wherein, the controller is configured to, in a test operation, obtain a temperature difference between a first temperature detected by the first temperature detection unit and a second temperature detected by the second temperature detection unit when the first temperature and the second temperature are in a predetermined reference range, the controller is configured to, in a heat storage operation, obtain a temperature difference between the first temperature and the second temperature when the first temperature and the second temperature are in the reference range, and the notification unit is configured to, when a difference between the temperature difference obtained at the test operation and the temperature difference obtained at the heat storage operation is equal to or more than the predetermined reference value, notify that a time for performing maintenance of the circulation circuit heat exchanger comes.