how can i fix my worcester 28cdi boiler?

You should have a white plastic key which fits into the filling loop assembly on the bottom of the boiler, once inserted you turn the key a quarter turn then open the grey knob (next to the filling point), to allow water to pass into the boiler. 1.25 bar pressure is about right. Your boiler should be OK at 1 bar so don't think increasing the pressure is going to make much or any difference to it's performance.

Martin
December 2008