Just spoke to a mate who's a plumber, he reckons it's the pressure vessel, can't find it on the parts list or on a couple of baxi boiler spare part suppliers, hopefully someone will have them, no idea how much it will cost though?
My 4 year old Baxi 105e wont hold CH pressure, topped up to 2Bar, eventually drops off after several hours. No apparent leaks on radiators but constant drip on overflow - anyone know what the fault is please