Thanks very much for the reply.

The trouble I have is that I am not confident enough to grow one from
scratch. Whilst I think I understand the basics and logic, the wiring
bit (e.g. use of PLC/ relays) is a bit beyond my comfort zone...

Also, from what I can see, I have an additional problem to yours in
that I need to run the UFH with seperate pump and actuators in
addition to all the zones.

Maybe I could split the problem into 2
- UFH
- Non-UFH

and wire the demand from each in parallel to the boiler? Not sure
whether that resolves the relay problem though - I'm not sure why I
need them at all to be honest...

thanks
Lee.