Hi and thanks for using 2CarPros.com. It sounds like something may be blocking the heater core. What I need you to do is allow the engine to warm up to operating temperature with the heater on high. Then, feel both heater core hoses. Both should be hot. If one is and the other is not, suspect a blocked heater core.
Here are several other things to check when it comes to no heat:
https://www.2carpros.com/articles/car-heater-not-working
Since the car overheated and you replace the thermostat, there could even be an air pocket preventing coolant from flowing through the core. In that case, loosen the return line from the heater core (the cooler hose) and see if you can burp some air from it.
Let me know if you have other questions.
Take care,
Joe
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Friday, June 8th, 2018 AT 7:18 PM