The display shows EE or E8 at times and then reverts to -22 and +4 but the freezer is constantly colder than -30c i.e. off the bottom of the scale of my thermometer. The fridge is displaying +4 but the thermometer says -2. Looking at other posts on this forum it seems I may need new thermistors but which ones – the green one – the yellow one ? How many are there and should I just replace them all ?