secondary control signal 260 the multiplying factor determining circuit 215 determines e g calculates the multiplying factor 240 used by the multiplier 225 of the feed forward loop 205 the multiplier determining circuit 215 is coupled between the feedback loop 210 and the feed forward loop 205 and more specifically between the feedback loop 210 and the multiplier 225 in the illustrated embodiment the multiplying factor determining circuit 215 includes a second pid controller 265 and a second adder 270 the second pid controller 265 receives the secondary control signal 260 from the first pid controller 255 and generates an error signal 275 the second pid controller 265 is coupled to the second adder 270 and sends the error signal 275 to the second adder 270 the second adder 270 is coupled to the second pid controller 265 and the multiplier 225 the second adder 270 generates the multiplying factor 240 based on the secondary control signal 260 and an adjustable variable further discussed below and sends the multiplying factor 240 to the multiplier 225 fig4 is a flowchart illustrating a method 300 of operation of the control circuit 200 to change a position of the mixing valve 130 first the differentiator 220 receives a first temperature from the first sensor 185 block 305 the first.