Heat blowing cold, no fix?

I've been trying to fix the heat in my car, but am a bit
stumped. When I turn the heat on, no matter what setting or
fan level, it blows cold.The car gets up to running temp,
maybe a bit below the mid line. Heater core was last
replaced about 5 years ago.Things I have tried/checked:
-add coolant
-replace thermostat
-hoses going to/from heater core are both hot
-make sure blend door actuator is functional

Any advice on next steps?