Liquid heater load control

A device for controlling the power consumption of a liquid heater having at least one inlet for receiving a heatable liquid having a first temperature, at least one outlet for removing the heatable liquid having a second higher temperature, an upper electric resistance heating element, a lower electric resistance heating element, a power supply line for delivering electrical power to each of the electric resistance heating elements, and a first thermostat for sensing the temperature of the heatable liquid in proximity to the upper electric resistance heating element and a second thermostat for sensing the temperature of the heatable liquid in proximity to the lower electric resistance heating element, each thermostat acting as an on/off switch that is open when the temperature of the liquid that it senses is above a set-point value and closed when the temperature of the liquid is below a set-point value, and the thermostats arranged so that when the upper thermostat is closed no heating can be done by the lower resistance heating element, said device comprising:

• detection means for detecting the amount of time the first thermostat is in the on state or off state, and for generating a first signal corresponding to the amount of time;
• controller means responsive to said first signal, and comprising means for determining a set-point value for an average heating rate of the lower electric resistance heating element;
• and
• power modulating means for modulating power to the lower electric resistance heating element so that the average power delivered by the lower electric resistance heating element equals said set point value.