Exactly my thoughts, look down in the near side footwell at the heater unit where the cable meets, the outer cable is held by a simple clip. I would first try and set your dash knob on full left (cold) and then with the outer cable retainer unclipped move the control and see if you can loose the heat, if you can pull out the slack and refasten the clip. You should get 5 clicks from one end position to the other as there are 6 holes in the mechanism for the sector to align with. Somewhere in the galleries is a photo I posted of the business end of the heater. Mine would not go on max heat until I adjusted it, not a hard job to do.
