The M021P will work in conjunction with any boiler system to implement close temperature controlled hot water system at mains pressure. It can be used to very economically and quickly convert traditional gravity fed hot water storage system into one delivering instantaneous hot water at mains pressure. Because the source of heat is independent of the control, the hot water cylinder could be powered by anything at all, gas, electric heaters, solar panels, coal, biofuel or any combination of all these.