Hi ,
I am having the same problem with my 306 misting up when the heater gets hot
.and it does get hot no problem there ...but the hot air will not be
directed to the screen for some reason

I took it in to the local Peug dealer .The mechanic took a quick look and
said the problem was the heater control box(  Matrix ? ) which is behind the
centre consol below the dash .
So it looks like I have to take the radio and consol out to get to the box
and then remove the box and replace it with another ?? or so they said .I am
not a mechanic !

Apparently what happens is the control dial for the heater box is stripped
off the and the activating arms in the box which are supposed to direct hot
air to the various parts of the car ,e.g screen ,footwell or the vents on
the front of the dash etc-- are broken ,and that is why the screen is not
getting the air it is supposed to get to keep it clear of mist !

I am not sure if these control-arms or  wheels behind the dials or whatever
in this box can be repaired ,but I doubt it .New ones are expensive so I
will try to pick one up at a salvage dealer .Has anyone got any advice on
this ??

Regards
Tony