I just got a second hand Opel Corsa a few days ago, yesterday i drove it for a little bit longer (35km) but while getting close to the destination and stopping at some traffic lights it started to overheat. I looked under the hood, the water was boiling but the fan was not working. So the fact that on the highway i had no problems it means that the water pump, radiator etc. are working fine.Can somebody tell me some reasons why the fan wouldn't start so i can check and find the problem by elimination ?