trouble overheating an heater not heating

Hello,

If your gauge shows overheating but the actual engine is not hot, then you either have a faulty temperature sensor or a bad gauge.
First check the temperature sensor. Good chance that is the issue.

https://www.2carpros.com/articles/symptoms-of-an-overheating-engine

If the heater does not heat, it could be for the engine not reaching operating temperature or a clogged heater core.
If the engine running at the correct temperature then it is likely a bad heater core.

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

I have attached the temperature sensor and heater core replacement procedure for your reference.

Please let me know of any questions.

Thank you.