Had a similar problem with my previous fridge freezer (although a different make!). Repair guy said that it was a faulty gas cyclinder - he said that they often can leak gas (although he said it wasn't a safety issue and I wouldn't have been able to detect it). It was located at the back of the appliance at the bottom. He re-filled the gas cylinder and it was fine. He said that it was a common fault when the equipment won't go cold. Just a suggestion for you!
Murphy
December 2006