Polo heater

[red griff roger]

Hi, sorry to jump into the VW forum, but a question for VW mechanics. My wife's Polo (53 plate, 1.4 FSI) has decided to have two heating options - freeze or roast. Can anyone enlighten me as to how the cabin temperature is controlled? Is there a sensor, or is it through the dial on the dash? If the dial, how does this regulate temperature? Is there a way of controlling flow of air (or water) and if so, where is the bit that might need replacing?

Thanks in advance chaps,

Roger