Just in case anyone else runs into this one. Turns out this may not be a very vehicle specific solution so read on!

 

The drivers side vent on my skoda (mk2 octavia FL) was blowing cold air on climate control. Scan with VCDS showed that the driver side footwell was reporting 87 deg. C, drivers vent was reporting 11 (likely due to the car trying to bring down the footwell temp). Other 2 vents were fairly normal.

 

I pulled the dash down from below (5 torx screws - 2 at the bottom, 2 behind silver panels and 1 in the fuse box). Then a further screw for some plastic venting.

 

I got to the sensor as as I tried to remove it (unclip then 90 degree turn) I heard a click. 

Turns out the clip had come out of the sensor a little bit resulting in a mis-reported temp.

 

Now the sensor reads a much more normal value!

 

I do have 2 weird rubber fin-type things that fell out though and I'm not sure where they fell out of but I've kept them. 

 

Update: It's reading bad figures again - I may change it as it's only £20 and then tape it in place.