No pressure in CH system

[mokanoo]

I had to remove two downstairs radiators to sort out the plaster work behind and switched off the central heating to be on the safe side. After sorting out the paster work I've put the two radiators back on, however, there is no pressure in the system (as indicated on the Valliant Combi boiler) and cannot switch on the system. The boiler indicates that the system needs topping up with water but need help on how to do this as there is no manual in the house. (recently bought)
thanks

 

[weargas]

which model vaillant? some have inbuilt filling loops.