Any updates on this anyone? I've just experienced a similar problem in my car today. Climate control set to 26 but still blowing cold air and the only heat i'm getting is from the heated seats - Not pleasant at 5am when it's single figures outside!
My car is a 2003 CLK55 AMG
Thanks guys, I shall get this part looked at and hopefully that's all it is. Any idea on how much a new heater valve is? I did find a link showing how to replace this yourself but not sure I like the idea of doing this myself so will look to take to an indy to sort.