hotpoint ff92 mistral frost free not cooling enough, not freezing ?

i've got a hotpoint ff92. filled up whith food after a shop and just won't get cold enough.same thing happened four month's ago and the nice man from hotpoint came and told me the thermosensors had bust,fixed it and took £90 off me.
is this a common problem and is there a way of by-passing them as a temp repair? the fridge get's upto about 15' and the freezer about the same. the refrigeration motor still kicks in, but the flap behind the light doesn't operate. any idea's apart from the tip?