All cars will steam up the windows with the heater left on recirculate for longer than about 10 minutes. Recirculate should only be used for the first few minutes to defrost or demist the windows...then switch to vent. However, Aygos are prone to water leaks, so if your car has leaked in at some time, and there is moisture or damp inside the car the windows will steam up. You should check in your boot where the spare wheel sits, as well as the front & rear passenger footwells to see if the carpets are damp or smell fusty