> I've also seen a system that used a pump and a thermostatic valve,
> plus a control circuit. Before you turn on the hot water you press a
> switch that pumps water from the (now cold) hot water line into the
> cold water line via the thermostatic valve.
That's a nifty idea. But why would the valve need to be thermostatic ? Why not
just a solenoid valve that only opens when the pump is running ?
Seems like this would be easy to build yourself, and removes the concern over
the hot water line being heated all the time.