First check your water level, if its low the water will not circulate fully,diesels do not overheat as quickly as petrol engines, make sure when the engine is hot that the top and bottom radiator hoses are hot, if they are check the heater hoses, they are normally at the back of the engine and go into the bulkhead together, these should also be hot, if not the heater matrix might be blocked, if your coolant has not been changed in a while, you may need a flush, finally check your heater control is actually working, the cable operates a vavle or a flap.
john jo, September 2006
