Abstract: A tankless water heater includes a sensitive flow sensor that has a magnetic sensor and a plunger with an imbedded magnet. The plunger is configured to lift in a direction of the magnetic sensor in response to the flow of water thereby changing the state of an output of the sensitive flow sensor. There are electric water heating elements situated within water heating chambers. The sensitive flow sensor and the water heating chambers are fluidly connected in series between a supply of water and at least one hot water spigot. In response to the flow of water, a change of the output of the sensitive flow sensor energizes the electric water heating elements, thereby heating the water.

Abstract: A flow detection sensor has a manifold with an inlet on a bottom surface and an outlet on a side surface. A movable partial blockage rests near the bottom surface of the manifold and is movable upward in response to a flow of liquid from the inlet to the outlet. A sensor detects the position of the movable partial blockage within the manifold.