Abstract: A flow channel switching system (1, 1?) including: a first on-off valve (10) which is disposed between a merging portion (6) and a branching portion (5) and in a raw water path (4); a second on-off valve (11) which is disposed in an outward path for raw water (7); and a sensor (13) that measures a state of water flowing through the raw water path, in which control is performed so as to open the second on-off valve and close the first on-off valve if a signal indicating that water is flowing in the raw water path is received from the sensor, then a signal indicating that no water is flowing in the raw water path is received, and then, within a predetermined time period, a signal indicating that water is flowing again in the raw water path is received.

Abstract: A water heater includes a bypass that is formed, on the side of a water supply pipe, branching from a main water path and bypassing a part of the main water path, and a flow path switching unit (a valve and a stepping motor) that is formed at a branching portion of the main water path and the bypass. The flow path switching unit is controlled by a controller and that can selectively switch a flow path between the main water path and the bypass. A microbubble generator generating microbubbles is provided on the bypass, the microbubble generator including a water agitator portion, a compression portion and a decompression portion. When the controller determines that scale has built up, the flow path is switched to the bypass by the flow path switching unit, and water containing microbubbles is caused to flow inside the water heater.