The invention includes a tankless liquid heater that employs a series of chambers, each having a plurality of heating tubes, with heating elements positioned thereon, and a control unit comprising a switch, controller, and power distributor to control the flow and heating of liquid in the system. In one embodiment, the control unit takes input from a liquid flow sensor that monitors the passage of liquid through the system, a temperature sensor adapted to monitor liquid temperature, and a current leakage sensor adapted to monitor the current leakage in the system. In response to these sensors, the control controller actuates the relay between an closed position, which allows current from the power distributor to pass to a plurality of heating elements, and an open position, which prevents the current from flowing from the power distributer to the plurality of heating elements.