Golf mk5 TDI BKD Heater blowing cold

[nathanrpile]

As title states, woke up to a fairly chilly morning today, hopped in started to drive, turned the heater on to receive cold air in my face.
Being a diesel it normally takes a while to blow hot after starting but the car reached optimal temp and still blew cold.

After 15 minutes of driving the car started to overheat unless the heater was turned completely off.

any suggestions to remedy or things to look at would be much appreciated.