Neff K4204XBGB/01 fridge warm

Hi gent need help with this fridge warm freezer ok but customer saying you can open fridge door and a large square ice on back wall of fridge defrosts and does not run again for hours the controls on fridge are 1 unit has it gone or could it have a system fault does it run of a sensor as i cannot see one on parts listing plus looks like freezer pipework starting to defrost when i went but could not get it to run (compressor) cheers alro