Been having this 'feature' for a while now :
Intermittent problem getting hot air out of any vent other than the ones at the bottom of the windscreen, which can be affected by using the 'control wheel' located between the two air vents above the radio on the centre console.
Problem is I can't find a consistent mode of operation. eg. Cold air from centre vents, so move the 'wheel' up to the 'Hot' position, nothing...., back down to the 'Cold' position, and hey presto, red-hot air. The next time I try this, it may or may not work, or it produces hot air in the 'Hot' position. This morning, no hot air in any position (apart from windscreen vents).
Obviously this 'wheel' is controlling some sort of flap / valve arrangement to divert air into the heater matrix, but does anyone know the detail of what it is doing / or what is likely to be the problem..? The behaviour changes only after turning the ignition off, and back on again - so something electrical involved as well...?
(Changed the Microfilter a couple of weeks ago BTW, so lots of air 'volume' coming out of the vents, just not a consistent temp...)