Samsung (Grey) American style fridge/freezer, switching off?

My Samsung (Grey) American style fridge/freezer with drinks dispenser not sure of model no. purchased from Currys, keeps switching off. I can reset it by switching off/on at the mains, but several hours later it will cut out again and temperature of both freezer and fridge increases to ambient levels. I tried a full minimum 48hr defrost as suggested on this site, but did not fix the problem. I've seen another thread possibly sugessting a thermal fuse ?
Also does anyone know where you can get a replacement water line filter.