In-car heating system (help)

I have a 1.3 1999 fiesta and having a problem with the heating system. When I turn on the fan and turn the heating switch on only cold air is generated - this is after I've driven the car to it's normal running temp. I have checked to see that the heating switch is connected. I'm not sure what else to check or do - PLEASE HELP.

The most common reason is that you probably have a faulty thermostat, which will be stopping the hot water from going around the heater matrix.

problem is most commonly, the heater control box which links to your heater, gets stuck because it doesnt get moved enough, because during the summer the heater is left on cold and never gets moved to any other position and then winter time comes and you move the temperature control to hot and the car still emits cold air, this is all caused by a stuck heater control box, located under the bonnet look at back of engine, by the bulkhead just below where the n/s wiper connects to the scuttle panel, plastic thing with two pipes at front with two also on the back of it which go through the bulkhead and into the cabin, also there will be electrical connector block on the n/s of it replace the unit.