Fan and Temperature light coming on straight away? Peugeot 106?

I have an x reg peugeot 106 independence and the problem i have is that when i start the car up from cold the fan kicks in within 10 seconds and doesnt switch off until about 6 minutes after i have shut the car down. I have had the temperature sensor changed, the ECU reset and a new radiator as the other one was leaking. I am now unsure what else there is it could be?