i have just had my combi serviced?

i have a ferrori 701 combi boiler, the heating works and so does the hot water, i have had to change the prv and empty the vessell of some water and the i used a foot pump to test the vessell to one bar
which was ok, but i noticed lastd night that the pressure had drop again below the 1 bar limited not allowing any hot water/ heating to get hot and al so come on, i have bleed the rads at times when the system is running and when it isnt running, what s else can you guys advice me to