Recently changed the house boiler   From Flexicom 24HX (24kW with a 2.4 Modulation - ie 10 kW min) (Set up as Y plan)   To Viessmann 100W 16 kW with a 5.0 Modulation - ie 3.2 kW min) (Currently set up as S Plan)   Both are "heat only" boilers but the Viessmann (once the rest of the parts arrive) will be set up to run DHWP   During the commisioning process the old Grundfos 15/50 pump speed lever sheared/failed and the pump was jammed on max speed. I was goi