I have a Fisher &. I have a Fisher & Paykel fridge/freezer model N500B a CFC model

Question

I have a Fisher & Paykel fridge/freezer model N500B a CFC model with the freezer below the fridge.We have started to get a frost biuld up at the top of the back wall of the fridge compartment. A registered repair man has suggested it is a know Fisher and Paykel problem and can only be temporarily addressed by melting the ice build up with hot water and/or a hair dryer. The build up seems to be increasing and i don't like the idea of using a hair dryer..doesn't seem to be a fully safe thing to do.Dave