The Efficient Home Forum

I believe that the Evohome controller will switch the boiler BDR91 relay for any call for heat, that is, for an S- plan system, if hot water calls, the controller switches both the HW valve via a BDR91 relay and the boiler relay and if a heating zone calls then the controller will switch both that zone valve via a BDR91 relay and the boiler relay. Both valves will have the grey and orange disconnected.

However, I'm confused as to what happens when an HR92 is added to the system. Does a call from a radiator controller just activate it's nominated zone, that zone being bound to the CH valve BDR91, and the controller switches that relay and also the boiler relay?
(I realise that in the given scenario, all radiators with open valves will also heat)

If you have HR92's on all radiators then you setup the system like the schematic on page 46 of the evohome installation guide with no heating zone valve - its just not required.