Thanks for that information Tony. I wasn't aware of this and the heating system supplier wasn't either. The pumps are as you said Grundfos smart UPS2 types .
Wired up this system in accordance with manufacturers wiring diagram. The system is heated by a gas boiler as main source of heat and has the option of using solid fuel to heat the cylinder also. On the cylinder there is a cylinder stat which is nominally set to 75 deg and this controls when the...