A valve assembly comprising a temperature responsive servo-mechanism adapted to combine hot and cold water under pressure to produce a constant preselected temperature of water at an outlet.The valve assembly comprises a housing having a valving cavity, a hot water inlet leading to the valving cavity, a cold water inlet leading to the valving cavity, and a mixed water outlet passageway leading from the valving cavity. A valve member translates in the valving cavity and divides the cavity into two auxiliary chambers. A passageway through the valve member allows fluid to flow from each of the inlets to the outlet passageway at a rate that varies as the valve member translates. Passageways in the valve member permit a portion of the mixed water to flow into the auxiliary chambers. An auxiliary passageway is provided between each of the auxiliary chambers and the outlet passageway. A temperature responsive element is provided within the outlet passageway. In response to a deviation in the temperature of water in the mixing chamber the temperature responsive element closes one of the auxiliary passageways causing the valve member to translate until the water in the outlet passageway reaches the preselected temperature.