Heater not working?

Hello,

There are few reasons for the heater to not function.
It could have a clog in the heater hoses or the heater core. It can also have blocked heater core. Another possibility is a stuck open thermostat.
When a thermostat fails at stuck open position, it does not allow the engine to reach operating temperature and this will affect the temperature of the heater, as it will not work properly.
If your vehicle reaches operating temperature then this can be ruled out easily.

https://www.2carpros.com/articles/car-heater-not-working
https://www.2carpros.com/articles/replace-heater-core
https://www.2carpros.com/articles/replace-heater-hoses

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.