I have a new Worcester 40CDI Regular Boiler that does not come with a built-in expansion vessel. I just discovered that the installer did not install an external expansion vessel either. For HW, I have an unvented cylinder which has a expansion vessel connected to its cold inlet though.
Our radiators don't heat evenly and some remain cold. Called in a plumber and he said that the original installer should have put in an expansion vessel for the boiler and that will solve my heating issues (it seems we've got a pressurized 'Sealed System' - sadly it's also missing a pressure release valve which he said he would install). I'm not convinced as an expansion vessel is essentially only to prevent backflow of water and is a safety measure (right?) and has nothing to do with additional flow of water in our radiators. I reckon it wasn't power flushed properly when the boiler was recently replaced as we've already tried balancing the radiators and that doesn't really help. Some radiators are boiling hot (at 70 degrees set for the boiler) while some are mildly warm.
Any advice? Should I proceed with the expansion vessel anyway (I reckon we still need one for safety reasons but don't think that'll solve my heating problems). Thanks.