LIEBHERR cpes 4613 fridge warm ,

hi guys this is causing me grief, i went to this and the freezer was fine , fridge not cold enough so i changed the air sensor in the fridge and same no change the compressor is on constantly now and the freezer has thick white ice around the walls , nothing on the back wall which has that aluminim looking crinkle panels , i see there is a valve at the rear by the compressor with an electrical connection , like the hotpoint bitron valves ?? any one have any ideas , i dont want to get a control board to find its a system fault fridge is only 4 yrs old cheers