Inserting a one-way/non-return valve next to Valve 1, orientated to only allow water flow away from the mains, would prevent the pump continually circulating if Valve 1 is inadvetatntly left one, say, after a power cut. In fact, Valve 1 could be replaced with a one-way valve so that water is still available, at mains pressure, during a power cut. Indeed, you may not even need to use the pump if the mains is up to it. One-way valves can be utilised to incorporate your tank too. Nothwithstanding comments regarding unreliable components, of course!