i served my apprenticeship many moons ago with the old scottish gas board and the training that we had was superb - went back to do contract work for them years ago and all they were interested in was how "much" business you had generated i.e. selling replacement boilers,powerflushes,alarm...
you,ll probably find that the hose connecting the expansion vessel to the block is chocked,depending on the location of the boiler (i.e. next to adjacent wall etc ) it is a simple enough job to do