Hello richard, firstly you need to check the condition of your water in the system, these boilers are prone to blockages in the pipe that leads to the expansion vesselyou will need to drain the boiler, and then release ther pressure from the expansion vessel. then clear the pipe with a peice of wir but make sure you release the pressure from the expansion vessel first, on completion recharge the expansion vessel first to 0.5 bar with the pipe disconnected. or contact a local corgi registered gbas installer or British gas. i have been to a few boiler that have been ruined by DIY repairs
Mark
February 2007