A thermostat for regulating temperature in a liquid, wherein the mixer comprises a chamber with separate hot and cold liquid entrances; a floating ball valve seated on the hot liquid entrance; a slit opening connection between the cold liquid entrance and the chamber, which slit is so directed as to cause the cold flow to assist in raising the ball off the hot flow inlet seat; a cylindrical, hydraulic fluid containing, flexible, elastic jacket surrounded chamber, wherein the fluid volume varies as to water temperature and a mechanical connection between the elastic jacket of the fluid containing chamber and the ball valve to force the ball toward the seat upon heating of the fluid in the temperature sensitive chamber.