Abstract: An instantaneous fluid heater having a combined safety shut-off and temperature regulator includes a hollow heater block having a fluid inlet, a fluid outlet and inner walls defining a plurality of interconnected heating chambers forming a serpentine fluid flow path from the inlet to the outlet. A separate electric heating element is positioned in each chamber and a separate thermostat is positioned at the downstream end of each chamber for opening and closing an electrical circuit in response to the temperature at the downstream end. An electrical sequence switching arrangement cooperates with the thermostats to sequentially energize the heating elements, beginning with the heating element in the most downstream chamber.