turn heater to hot only cold air.i was told it is the heat exchanger how difficult would it be to replace.and how much. many thanks. here is hoping.

could also be air in cooling system, or thermostat faulty

Sound like something which l experienced lately as well. l have the heater running for sometime and it started working.

You would always ring up your dealer asking them over the phone. l had done that in the past but did not have time to at present.

u could have a blocked heater or lack of coolant could also cause this problem. Air as well
If coolant is OK go for a 2 mile drive making sure the engine has warmed up properly lift the bonnet & u should be able to see to pipes leading to the heater put ur hands on them, if they r cold, or one hot & one cold there is no flow to the heater the heaters blocked. To unblock u could connect a garden hose to the heater & flushing it through, making sure the other end is open so u can see the water passing through If the pipes r difficult to disconnect from the heater u could disconnect them from the engine side.
should this fail, it is well blocked. so the last resort we need a bit of pressure, with one hose filled with water attach a bicycle pump to the other end & the pressure should force the water through. l did this on one heater & never had any more problems Good luck