Convert Combi to unvented cylinder setup with Evohome

Hi, I self installed the evohome system (thanks Evohome shop) on my Combi Boiler system with 12 radiator zones last December, it has been excellent and I found it easier to install than I expected.


I have never been happy with the DHW flowrate from the Combi (its a 2006 35kW Worcester Bosch CDI combi), I am now thinking of converting the set up to an unvented cylinder with same boiler for two reasons:

a) Get better flowrates to shower
b) Fit solar heating to cylinder in the future.

With the unvented cylinder , I will add a two port zone valve from the combi heating central circuit + the Evohome heating kit .

Is my understanding of the control correct/possible:
a) If the hotwater sensor temperature is below setpoint the controller sends signal to new Hot Water Kit BDR91 to open the inlet heat zone valve to Cylinder , and b) The controller will also send heat demand signal to the original BD91 relay that controls the boiler. I should not need any new control wiring into the boiler.

b) Do I have to combine two of the radiators to single zone , to allow the addition of the hotwater kit on cylinder as a zone.


Thanks for your help