Falling Pressure?

Each year at this time when I turn the heating on on my Linea 24 combi boiler after being off all summer, the pressure will drop and I am left without hot water or heating until I get someone to come to it. It is situated in loft and the handle to the inlet valve for repressurising is very stiff so I am scared to do it myself. No problem with hot water all summer, it only happens when I switch the central heating back on.
Can this problem be avoided?