faulty heater fan in Peugeot 405 SRTD 1995 model?

Started the car yesterday and heater fan came on straight away and I could not turn it off. It is not running at full boar when in off position and will increase in velocity as it should. Is annoying especially as its winter here in Snowy Mountains , Australia and its cold enough in morning without the fan coming on straight away. Must be a fault with the fan speed adjustment but really have no idea. Any guidance would appreciated. Cheers