Abstract: A thermostatic control valve assembly for use in continuously mixing a hot first fluid with a cold second fluid to continuously produce a mixed fluid at a constant temperature. The valve assembly includes an improved baffled mixing dome defining a mixing chamber that facilitates thorough mixing of the hot and cold fluids over a wide range of flow rates. Also included is an improved multiple response thermostat having a fast response rate adjacent to the entrance of the mixing dome for responding quickly to the temperature of fluid entering the mixing dome. The valve assembly further includes a piston/cylinder configuration which covers and uncovers internal passageways to control the mixed fluid temperature. The internal passageways are shaped to cause a non-linear change in the mixed fluid temperature in the mixing dome as the piston moves in the cylinder.