No Heat - Everything Else Normal

[EThirD]

My GF has an '04 non-S Cooper CVT. She's got no heat at the moment. Dummy gauge says coolant temp is nominal, she tells me coolant level is good (I can't get to the car right now). Anybody have any thoughts as to why she'd have no heat?

[GreenBMW325is]

Air in cooling system, coolant leak some where either the lower corners on radiator wep hole on water pump or thermostat leaking, clogged up heater core due to incorrect coolant being used.