CLK 230 1999. New to me. Heater problem though...

[Boffo]

Hi.

I've just got hold of my first mercedes. A 1999 clk 230 and I love it.
Except for two problems.

Even though the blower works well with plenty of power, there is no heat.

Does anyone know anything about this problem, is it common?

Thanks for any help.

Paul.