I have an 02 Focus 1.8 TDCi, last week the heaters decided to start playing up, not blowing hot air into the cabin, so up to now I have replaced the thermostat, replaced the water pump and the auxiliary drive belt,I have removed every water pipe and flushed them through, flushed the heater matrix out twice, put it all back together, topped her up with coolant and bled the system of air, now I only get hot air out of the heater when the car is being driven, as soon as you let off the revs the heat drops down to being just luke warm. All the pipes get hot the car has never overheated and I am stumped now. Please somebody help me, I know its not the end of the world but I have spent the last 4 or 5 nights messing about with it and I'm going to end up putting a hammer through the windows pretty soon