Hi,
According to Refrigeration Engineer (http://www.refrigeration-engineer.com/forums/showthread.php?t=14614) the thermistors are embedded and are not replaceable. I have the same model not even 4 years old with the 'high freezer temp' light on, freezing in fridge, freezing then defrosting in the freezer. Independant fridge engineer (without seeing or knowing which model it was) reckoned about £200-250 just to strip down, re-gas, replace condensor etc. Apparently Hotpoint models are well known to 'die' around the 4-5 year age. Won't be buying another Hoptpoint!
Hope this helps
Martin
Martin, April 2009