Heater control Defrost Position

I cannot get the distribution control knob to the defrost position on my 2003 TD4. It springs back slightly when I try to obtain demist/defrost position and there is little hot air coming out of the windscreen vents. It appears there is still a large proportion of heat being deflected to the floor area. This is a bit frustrating when trying to defrost on a frosty morning after running the engine for 10 or so minutes to get a bit of heat into the coolant system.

Get your head in to the passenger foot well and look up - there's your heater/fan. If the control cables have come out of their clips you can get this problem.

You can also get this problem if you have changed the head unit and the wires drop down onto the heater control.

Thank you to both of you who have kindly answered my query. Strangely enough a local Land Rover garage changed the Imobiliser Ecu some time ago that unit is beside the radio so there was a lot of dismantling in that area and it is more than probable wiring could be causing the problem.