Seems like a common problem with the APM6855, likewise my fridge stopped cooling yesterday (Hottest Day of the year nearly)
but the freezer was ok and it too is only 13 months old.
I prised out the plastic cover at the back of the freezer compartment and pulled forward the freezing element cover that houses the circulation fan to find that there was quite a bit of ice surrounding the element.
I switched off the fridge/freezer completely, defrosted it overnight, started it up again this morning and it is now running great again. I am unsure if there is an underlying fault with a heating circuit which should reduce the ice build up surrounding the element. I'll check the element again in the next few months.
I was thinking that the problem lay with a faulty thermostat initially as well, I'm glad I read this thread first.