Mine used to do the same. Had 10 mini radiators and it could never reach them all! Would over pressurise, then go really low having to be topped up. Was in the process of getting quotes to fix it, when it broke completely - pressure went to 0, then it spat a load of water out of the emergency valve, before starting to hiss, followed by a very strange noise which sounded like it was going to blow up so now have no heating or hot water. Just got a quote for a valliant 831 as a replacement (was told the Worcester we had was known for pressure issues due to a condensation issue and although it could be fixed, the parts were too expensive to make it worthwhile and i was better off getting a new boiler??).
Sel, January 2010
