Larder fridge APM6321 not cold enough - what is the likely problem?

Hi,

I have a APM6321 Larder fridge built inot my kitchen alongside the freezer APM6222, the fridge is not cold enough even when I set the thermostat to 5 food is not lasting very long. I have put a thermometer in which varies between just being in the acceptable range for a fridge and being too warm. The fridge has lots of clearance around the vent for air circulation and the drain hole is clear under the salad crispers. Any ideas on what to check next and how to check it?