HMMN, id be inclined to say the ntcs were faulty
have you noticed your fridge temp dropping?(that probably why the temp alrm sounds)
its usually the ntcs to be fair , id hav to recommend a service engineer to fit them , as it does involve removing the cooling evaporator from inside the top of the freezer, and inserting the ntcs in the evaporator, and theres lots of sharp edges
there was a post about this not to long ago, but in all honesty it aint as easy as the guy says, trust me, ive been cut many a time!!
given the quality and price of your appliance, id say it was a worthwhile repair, and would probably cost less than £100 (although, it depends on who u call out, obviously)!