Did you blow it when changing the heater tank? Is there a cycle?
But it doesn't matter. You can take down the two warm water pipes in the engine compartment and try to see if there is any blockage.
The second is whether the control panel of the air distribution box moves when it is controlled. If it doesn't move, there is no warm air.
Generally, the thermostat is not considered, because if the thermostat is not turned on, your water temperature will be very high and the water will be boiled.
According to your description, these are the results of fault analysis.
But it should be noted that there will be no warm air in the cold car. You can't expect the car to have heating as soon as it starts. You must wait until the water temperature rises.