cdjr - i noticed your in the bucks area - if you near Milton Keynes pop over..
If you come over to Milton Keynes their is a local renault specialist who can regass and check your system for £29.99. Just don't tell Renault you went there !
This deal only applies to Sundays and is around £40 all other days ( which is still pretty good )..
It is normal to expect to regass the system every two years which is why Renault have told you that but I dare say they weren't too good about the communication side of things..