Abstract: An instantaneous fluid heater having a fluid heating chamber including therein a plurality of electrical heating elements. The supply of electrical power to the respective ones of the electrical heating elements is controlled by a solid state switch which is gated by a zero crossing trigger device to supply power to the heating elements. Each of the trigger devices includes means for comparing a control potential and ramp signal potential coupled to them to selectively gate the solid state switches to energize the heatiing elements in response to the comparison of the potentials. In this fashion, all of the heating elements are not turned on at the same time, and undesirable light flickering and unacceptable disturbances in the line voltage is eliminated.