BMW Repair: E46 heater not blowing hot air, air flow sensor, circulation heater

Question
Hi again Evan

You kindly helped me fix the previous problem below by suggesting I replace the Resistor unit, which worked a treat;

I have an October registered 2000 model BMW E46 318Ci which has Automatic Air Conditioning Control. It seems to have a mind of its own and sometimes will blow air in to the cabin and then stop and start erratically. I've cleared the control panel grille and the internal small fan unit of dust, checked the heater motor and unplugged/re plugged connections, but no improvement. Before I go replacing the control panel is there anything else I've overlooked?
Regards John.

However it has now stopped blowing hot air (it is blowing just slightly luke warm), despite the two pipes going through the bulkhead to the heater matrix being nice and hot along with all the other pipes. This problem started after I had to replace a plastic coolant pipe on the side of the engine block a few days ago. I've bled the expansion tank OK and the cooling fan kicks in OK and the temp gauge is reading normal. Could this be the resistor again or something else this time?

Your expert help would be appreciated again.
Many thanks
John

PS  In just the last few months I've also had to replace a sticking heater valve, a leaking thermostat housing, a split in the expansion tank and I have been told that the air flow sensor needs replacing (engine management light is on) and the oil level sensor in the sump is playing up. It seems that a lot of inferior quality plastic parts seem to be being fitted nowadays, which is a shame as it's damaging the reputation of BMW for reliability :-(  

Answer
John, I would look to coolant level being proper filled, water pump circulation, Heater valve (temperature drop from in front of valve to behind valve.) Also make sure the valve is plugged in. With the engine at operating temp. and the A/C to max hot with the thumb wheel in center vents set to hot, the inlet coolant hose to the heater core should be screaming hot. Also make sure that the cable from the center vents to the duct is working. I have dislodged a couple doing Final stage resistor jobs when removing the footwell duct. Frankly this sounds like a low coolant problem or an air bubble trapped in the heater core.
-Evan