You need 5 cores between the boiler and the wiring centre . Live , neutral , earth and a supply to the valves and a switch wire back from the valves . These last 2 just come from where the room stat link is fitted in the boiler , the link may not be mains voltage but this does not matter as it is only being switched by the valves.
Basically from the spur you need a supply to the 2 channel clock and a supply to the boiler , the live out of channel 1 on the clock should go to the brown of the first valve and the supply out of channel 2 should go to the brown on the other , (after going through stats) , the blues are neutral and cpc is green yellow .
Where the link on the boiler for the stat was removed you need a pair from there , 1 side going to both greys from the valves and the other going to both oranges from the valves .
That's it, when you turn a channel on , on the clock it will power up whichever valve and open it closing the micro switch inside and connect the grey to orange and fire the boiler as it would do if the link was still in the boiler.
(Some boilers do not have a link to remove , most do ) this should get you sorted anyway , if your still unsure just let me know what boiler it is and ill tell you where to connect it .