Coolant warning problem

[easylife]

I have a 2nd Gen Turbo Convertible and recently the coolant light comes on when I start the car cold and only goes off once warmed up. It then comes on intermittently whilst driving for a few seconds at a time.

The coolant levels have been fine all the way through and the car does not drive any differently.

Any ideas what the problem is? Dodgy sensor (if so which one)? Or something more worrying?

Look forward to your input.

Cheers
easylife