Ford f150 heater probs

heater does not work can anyone give me ideas of what is wrong please. my heater core was leaking i unhooked it stayed un hooked for several months i hooked it back up now i have no heat i flushed the system for blockage that didn’t work.

You don’t say if the heater core is now replaced or not and the hoses hooked up properly.

If it is repaired, there may be air in the cooling system blocking circulation.

What year is it?

i didn’t replace the heater core couldn’t afford it right now so i hook the old one back up how will i know if it is hooked up properly