Never flushing & replacing your anti-freeze/coolant...
Corrosion.
You prob have to replace the heater core
No heat when you turn it on in the car.
Heater core may be air bound and have to be bled Heater core may be plugged or restricted Thermostat may not be opening allowing coolant flow to core
leaking heater core
Most likely a bad heater core
Heater core failure.
Bad heater core. Its a pain to replace. get a Hanes manual if you wanna try to do this.
Check inside the car undre the dash , check the heater core.
Heater. Core
bad heater core.
Check the heater core if weather not responsible.