open the freezer door and look through the grill bit in the very top of the freezer compartment.if it is a solid lump of ice especially at both sides then this is likely to be your problem.to mend it is a bit involved but it will either be a faulty defrost heater or a faulty evapourator sensor.to tempary fix it defrost whole appliance by unplugging it for 24hrs and leave both doors open.then switch it back on.if both parts work again then it points to one of the above mentioned problems.repair cost around £80-£100
ck, April 2009
