Vauxhall Corsa radiator cooling fan starts almost immediately

Only had second hand car for a few day, so still under warranty.. The radiator cooling fan comes on not long after the car has been started and stays on. The temp gauge on dashboard stays normal. Dealer has looked at it and apparently tried a new switch but no change. They believe it is just an 'over-cautious' cooling fan. I guess an 'over-cautious' fan is better than a non-working fan.. but could this be masking a bigger problem? Could a fan that is almost permanently on cause a bigger probelm later? Or need replacing by me later out of warranty? Any advice appreciated.