oldscoobye

Hi, anybody got any ideas on heating issues with C5 HDIs (SX) I have to set the temperature controls (dual control model) to 28 (Maximum) before I get anything resembling heat from the vents and even then it is only luke warm. I have also noticed that the outside temerature reading in the trip computer displaying is reading a mimimum of 10 degrees higher than the actual outside temerpature. Are the two related? Any advice greatfully received. The car is a 2001 model with only 34000 miles up. Cheers