Fridge not cooling down in my Hotpoint FF92TC fridge/freezer?

Hi, The freezer section works normally but the temperature in the fridge section rises to +19. I was advised by an engineer to swith off everything for 48hrs to see if that made any difference.It did for acouple of days then the temperature shot back up again to +19. He has now suggested that it could be the control module YIKES £140+vat +time. After looking at some posts on here does anyone think it might be a thermistor problem? If so were is the one for the fridge section?
Thanks for any info