Below the boier there are two valves capped off, one with a blue handle and one with a red handle, (pic 6) you remove those caps and fit the filling loop hose between the two and open both valves, the hose will be lying around somewhere
Good enough boiler, but I think main make the exact same boiler but quite a bit cheaper @gas112 is the man to advise you better, I have tagged him for you so hopefully he will be along soon to give you some more advice
I have had exactly that fault and it was a tooth on the synchron motor that was sheared off, either that or the synchron motor is not fitted properly and is jumping the gear mechanism
Personally I would just pick them up when in screwfix or the like or order online, would never think of going into a shop just to buy a pipe slice, cant see your idea taking off