I just got my Vortech MP40w ES in and I installed it and my knob does not work at all either. I ended up having to slip the knob off and use a pair of pliers to turn the little clear peg the knob is supposed to turn. Very poor design for 299.00 dollars. But its a great concept of a product. Just that darn knob does not work to turn up the flow or turn it down. I would recumbent the product but Im sure disappointed the knob doesn't really do anything unless you take it apart and use pliers. Sucks