my pressure keeps dropping below the 1 bar mark?

i have just had my boiler services and the gas engineer has just fitted my ferroli 701 boiler with a new PRV he said that there was some water in the expansion vessell which he drained down and used a foot pump to pump air in to the vessell up to 1 bar
the bolier has been working fine for the last week but noticed that the boiler has began to be more noisy again and noticed that there was water again at the base of the boiler, but theres not water leaking or any condension, the nose is like a woosshhing sound and the pressure has began to drop again
have any one got any ideals to correct this problem