in work at the mo, so not sure the exact model of boiler. As far as I can remember it's a Baxi, is free standing in a downstairs cupboard, with fairly easy acces to all pipework.
Sorry can't be more technically accurate
I've got a problem with CH radiators heating upstairs, when CH is turned off, and hot water is turned on. I believe this is a common problem with gravity fed hot water systems.
I believe the cause of this is that the CH system is as good as acting as a gravity fed heating system itself...