I Have a Worcester gas system that is suffering pressure loss any DIY repar?

HI MATE ITS ROBBO THE PLUMBER.
PRESSURE THE BOILER AND TURN ON. GIVE 5 MINS AND LOOKOUTSIDE BEHIND BOILER. THEIR IS A SMALL COPPER PIPE BELOW FLUE. WHEN ON , LOOK IF ANY WATER DRIPPING OUT. IF YES A SMALL PIPE IS BLOCKED LEADING TO EXPANSION TANK. TRY THIS FIRST . PROCESS OF ELIMINATION .ROBBO P.S REPLY WID ANSWER

ROBBO
January 2009