I'd really like to make an on-demand water heater to replace my HLT eventually. The original plan was to mount a PID probe into the top of the heating tube near the unrestriced outflow, set my desired temp and control the input flow manually so that I don't under step my temp. However, I thought it might be even more slick to invoke a flow control valve so for strike water and run the element at 100%. My plan A would work OK for me because the flow rate isn't that important to me but if I find a cheap enough flow valve, I'd give it a try. Anyone know of any cheap sources? Many hundreds $$$$ from what I've seen.