Most common causes are either a blockage or an air lock.
Give the cooling system a good flush through with the thermostat out, it's in the middle of the car under the drivers side inspection hatch. The drain plugs are underneath the car roughly in the middle around the drivers seat and one at the bottom of the radiator.
Refill with roughly half and half antifreeze and deionised water.
Make sure you get all the air out as these are a nightmare to fill, should take around 12 litres to refill in all.
Mince, December 2008
