Flow switch? I thought there might be a safety device like a limit switch or cutoff if the circ gets hot before it overheats, guess not The little pump works 24/7 in the overall system. Different than the big jet pumps. Circ's have a flow switch in line (what is a "Paddle Post" type switch), note the flow direction indicator as the post will precede the paddle in that given direction, epoxy incapsulated with wired lead attached to main control board), located inside a clear or white 3/4 inch "Tee Fitting", can have a barb or treaded configuration for input and out put. pre heater and some post heater and circ pump, depending on your brand. I am working on a Dim1 19 Dual Temp circ pump R & R. Bubble patterns, if your getting some is important. If the units hot, it might be time for a replacement. Did you find voltage at the leads