No heat, air blender might need to be replaced.

If your climate panel works fine, but the air just isn't warm, it's probably the thermostat. I'm not as sure on the 1.8T engine, but I can guarantee you that a stuck thermostat is very common on the 2.8L V6 engine. I changed mine three weeks ago, and have done seven or eight of them in the past. It's very labor-intensive (the front of the car has to come off), so you may as well do the timing belt as well. I'd bet a shop will get you for 5-6 hours' labor. If you're in or near upstate NY, I can do it. If not, find an independent shop that specializes in European cars. Use a dealer as last resort only, as they'll get you for $100-120 per hour.