Page 26 does give a diagram showing the three 24v cables. However to see how these are used one has to look at this PDF and it would seem the 24v supply is all connected with the ebus and uses a VR30 board.
This it would seem changes the speed of the pump and is rather complex and I would not want to mess with these connections.
I have the same boiler - The sbus supplies power and data over two conductors. The 3 '24v' terminals clearly show "Do not use". The sbus can control many things, and also reports other things to the remote screen, such as icons for pump run, flame lit etc. Quite good really.