There are several possible causes for your no-heat problem.
(1) there may be air trapped in the heater core. If an air pocket becomes trapped in the core, it will prevent coolant from passing through the core so it will not get warm. You can try disconnecting a heater hose and pouring antifreeze directly into the hose leading to the core; if this does not work there is a cooling system vacuum filling tool called an airlift that fills the cooling system under vacuum to eliminate air pockets. The tool costs around $100 and requires an air compressor to operate, or many auto shops can vacuum fill the cooling system for you.
(2) Your heater core may be blocked with deposits. If so, replavcing the core is needed to correct the problem.
(3) You may have an internal door problem inside the heater case. If the doors are not in position to direct airflow through the heater core, the air will not be heated.
Feel the inlet and outlet hoses at the firewall; if both are very hot then the coolant is flowing through the core and the problem is inside the heater case. If one hose is hot and the other is cold or only warm, then coolant is not flowing through the core because of air or blockage.
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