I've had 4 Corsas and everyone of them done exactly the same - until one day on the last one the gauge wouldn't go down when i was driving along on a fairly cold day indicating the thermostat had stuck closed giving the high temperature. If yours is one of the older ones that has a timing belt and the mileage reaches around 80,000 when its due its second belt change I would suggest changing the thermostat at the same time - only costs a few extra pounds. The themostat sits in behind the timing belt.