I am not sure where you are at on the fault tree. energising the diverter valve is already happening as this is what the wax capsule does and produces CH.
I've not had this problem myself so take the thoughts lightly - suggest you take the wax capsule head off again. This being to retrace your steps ie the DHW was working before the capsule was changed. So in changing the capsule something is now not quite as it should be. It's possible of course for a 2nd fault to have just happened but unlikely.
Looking at fig 2 in the manual (flow schematic) and fig 22 the horizontal pipe going into the wax capsule head is directly from the cold mains (item 91 gasguru stated). suggest with the head off
1) very gently turn 91 water mains to on and see if water passes. get ready with a bowl as i am sure it will come at pressure
2) blow into the corresponding inlet on the wax capsule head. air should come out of the vertical outlet really easy. there should be no air coming out anywhere else
If these work then i think the diverter valve is working ok
Next
3) open a hot tap and with a piece of plastic pipe seal with your hand inside the vertical pipe blow into it and air should pass
if it does then i would think there is no blockage. No further ideas other than there is a DHW manual flow restrictor that can be adjusted with an allen key (fig 13 in the manual) but i am not convinced as you had DHW ok before and that has not changed.
Are all the wires on the various components - sometimes its easy to knock something off without realising?