When you say you have the extended warranty, VW have a range of warranty products and the cover will differ from product to product. So whether or not your warranty covers your issue may depend on its scope of cover.
- VW’s stand alone extended warranty product where you can select either All Component or Named Component cover
- VW’s All In product which also includes servicing, MOT and breakdown cover
- VW’s Approved Used warranty
So maybe check the small print in the warranty booklet for your specific warranty to see if it would cover failure of and / or defective components of the heating and ventilation system. Presumably heating and cooling from the front vents for the driver and front seat passenger is working as it should?