I'm used to my heater only working on number 3.

However if i turn it below that it just goes off completely and wont work. I have noticed if i take the car upto around 6k rpm the heater springs back into life on the 3rd speed

Could anyone explain this?

The revving thing's a bit bizarre, but chances are it's the pull down resistor on the heater matrix.

Pic in this thread - http://www.clubpolo.co.uk/forum/index.php?showtopic=12474