please help! dont know what is wrong. replaced thermostat and bled lines and still no heat. What else is there.Desperately needing help.

If there is no air in lines, you may have a clogged heater core.

Heater is not working, checked thermostat,heater core is fine, checked fuses. Took off dash, couldnt find anything. Behind heater panel it is electric could not find anything. I really need some help. We had to buy a little dash mounted heater/fan blower. It works a little but when it gets 20 below. This car is going to be an icebox. Please help