Our Miele chest freezer model GT 315 ES is showing error code F4 which, according to the user guide, indicates a 'technical problem'. I've read that this currently displays when there is a fault with the 'sensor evaporator'. However, our freezer is old, so I'm not sure if this applies. Can anyone confirm what the problem is likely to be, whether any necessary spare parts are still available and how easy it would be to fix? Thanks in advance for your replies.