E39 528i no heat after overheating engine

[TheFakeBigD]

Hey guys I'm an independent mechanic who loves Bimmers and I'm looking for a lil help because I am stumped. I have a customer's 528i that he overheated on the highway. His expansion tank blew out so I replaced it as well as his thermostat & now the car has no heat. I know the bleeding procedure so I don't think an air pocket is the issue as I have no air coming out of either bleeder. I even tried driving the car for a few mins & bleeding it running (which I know many people from upon but it has worked for me many times in the past). At this point I am genuinely stumped & any insight would be very much appreciated as I have never had this problem before.

[Benny771]

Water impeller broken ? Apparently the plastic ones do this.

[KevinMullins]

Did the expansion tank blow due to age or is there an underlying cause? (ie clutch fan, water pump, etc)

For now I'm assuming the engine comes up to temp just fine, temp gauge shows normal, etc, etc...

Are the coolant lines leading to the heater core warm?
Is the AC on for some odd reason? (which would kill the heater core solenoids)
Have you tried cycling the air vents to see if its a flapper that's not working? (manually select defrost, upper, lower, middle, etc)