Abstract: A device for limiting the temperature and pressure of a fluid by controlling the electric current to a heating element. The device includes a cylinder connected with a tank in which the fluid is heated and includes a pressure responsive piston movable within a cylinder against a compression spring opposing movement of the piston. The piston is tapered to a conical or somewhat pointed shape at its lower end to allow a faster escape of fluid from the tank and to guide the piston into an opening in the tank to achieve a thorough seal when the pressure in the tank has been relieved. The cylinder has a discharge opening threaded externally to which is attached an internally threaded discharge pipe, the threading being such that the installer cannot jam the pipe against the piston and thus stop its movement. When the pressure exceeds that for which the spring is designed, the piston compresses the spring and operates an actuator for a microswitch to break the electric circuit to the heating element.