Proline fridge freezer PC213NF

Hi all
Got this fridge freezer thats driving me mad! When you switch it on it will run for a short while until the back wall of fridge just starts to frost then cuts out, before theres any cooling in the freezer coil. It will come back on as the fridge warms but will cut out again. I thought it could be the fridge thermistor but all wires coming to the module are moulded into the insulation of the fridge and comet don’t list one anyway. So i sent off the module to QER, its the one that fits in the housing on the cieling of the fridge and has the lamp holder and lamp switch all incorperated in it. They sent it back repaired but when fitted it made no difference. They sent me out another, which when fitted seemed to have solved the problem, the fridge and freezer got down to temperature and was running fine…. for about 24 hours and then cut out again and resorted back to origional problem. surely i couldn’t be unlucky enough to get 2 dodgy boards. Now yesterday i went out to an ocean APM6825 intergrated fridge freezer which has exactly the same board and problem and i’m now at a total loss as to what to do. Please somebody help me as i don’t have much hair left to pull out!
Thanks Subs:?