i just had a brand new heater core put into my civic, and its still blowing out cold air. any idea what could be wrong?

 

Sounds like maybe a thermostat problem,when you put the core in did you make sure the coolant is leveled off? I'm assuming you checked and make sure everything is connected properly.The thermostat is not hard to replace and not expensive,just make sure not to overtighten the bolts on the housing and place the thermostat right side up.Good luck. Oh and don't forget to open the bleed screw on the housing.