Abstract: A temperature controlled valve assembly which comprises a temperature sensor for sensing variation in temperature of a mixed fluid of hot and cold fluid mediums, a proportioning valve member for regulating the amount of flow of the hot fluid medium relative to the amount of flow of the cold fluid medium in such a manner as to increase the amount of flow of the hot fluid medium to be mixed with the cold fluid medium when the temperature of the mixed fluid increases over a predetermined value and to increase the amount of flow of the cold fluid medium to be mixed with the hot fluid medium when the temperature of the mixed fluid decreases below the predetermined value, and a power piston for operating the proportioning valve member.