Heat is not blowing as warm as before replacing heater core

Good afternoon,

Did you get all the air out of the cooling system?

Try running the engine at 1200 rpm for five minutes with the cap off. Watch the coolant level and see if you get heat. If you do, it had air in the system.

If it does not then it may be the blend door, but doubtful if it worked before the repair.

Roy

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

As the engine operates, any air trapped in cooling system gathers under the radiator cap. The next time the engine is operated, thermal expansion of coolant will push any trapped air past radiator cap into the coolant reserve/overflow tank. Here it escapes to the atmosphere into the tank. When the engine cools down the coolant, it will be drawn from the reserve overflow tank into the radiator to replace any removed air.

Sounds like a plan.

Keep us updated.

Always glad to help.

Roy