Have to rotate the knob to the heating position, see the picture .

..only it's not quite that position (the wonders of marketing pictures eh!?). It's actually right the way around, opposite the 0, as a previous poster mentioned. If the symbol was where that actual click-stop is, you wouldn't be able to see it when sat in the driver's seat.

OK, this picture is from car with driver seating on left side .

I guess, that everything is symmetric in opposite case :P.

I find asking the mother in law to breathe on them is more effective