Evohome with Vaillant Boiler

[MikeJJ]

My Honeywell Smartfit low voltage system controller has failed and I am considering replacing it with an Evohome system.
It is S Plan and both zone valves are to be changed for 240v units and will be controlled by BDR1 relays.
I have a Vaillant Ecoflex Plus system boiler. This boiler also includes the system pump which is controlled by the boiler controls.
My question is: how do I connect the zone valve controls to the boiler. At the moment the Smartfit box is connected to the boiler using a 4 wire (3 core + earth) cable which also supplies mains to the controls. The BLACK wire is connected from the SL connector in the Smartfit to terminal 4 on the boiler terminal block. (Vaillant unhelpfully just use numbers on the terminals)
None of the Evohome installation diagrams that I can find shows this configuration. Logically the ORANGE wires from the MVs should be connected to terminal 4 - is this correct? If not how does the demand get to the boiler or will I need a separate Evohome relay for the boiler?

[Richard]

In this situation, I would use a 3rd relay as a 'boiler demand' relay and you won't need to use the orange wires to switch the boiler then.

The BDR91 is capable of switching both 'volt free' and 230v boiler connections, which I know the Valliant has.

I hope that helps.