Abstract: An electromechanical control system that quickly and accurately controls the flow of two primary fluids such that the mixed secondary fluid would be delivered to an end user, such as a shower or bath or the like, at a constant temperature. The invention allows the user to select the temperature of the secondary fluid via a digital control interface. A temperature-sensing element located in the secondary fluid provides a feedback signal to the control electronics. Upon flow of the secondary fluid, the control electronics determine the required flow for each of the two primary valve members and control said flow from each primary valve member via an electronic signal. The output signals control two high flow proportional solenoid valves such that the primary fluid flow is electronically adjusted through a plurality of positions from full on to full off. This constant control algorithm provides quick, accurate, and stable secondary fluid temperature.