Brand new thermostat, back flushed and flushed heater core about 6 times, blend door moves just fine but i'm not sure if the door closes all the way, airflow coming out is great(just cold). I've even tried installing a valve on the coolant line that allows the coolant to bypass the heater core so i could decrease the flow through the bypass. I've checked all these things and yet still no heat, any ideas?