How do I get heater to work always blows cold air? on 2007 BMW 328i

Heater does not work properly. Blows cold air most of the time, even on the highest setting. Air on a couple of occasions became warm never hot.

Asked by for the 2007 BMW 328i
Have you adjust the stratification wheel in the centre of the dash? Possibly faulty heater tap or mixture flap in the heater box
2 more answers
Turned out to be a bad thermostat.