hey there people! found out why i could not fill system pressure on my b/w 24cdi it wasnt the filling key or the filling valve assembly, but when i took the assembly out only 5 min job! there was a build up of what i can only say as carbon it was solid and hard where the assembly connects to the inlet housing it was totally blocked so no water could get through. a little gentle poking and wohoo freed it water flowed out!! refitted the asembly and refilled problem sorted! hope this will be helpfull to any 1 with this problem!!