pymagnet

2 days ago my eng check light came on. Took it back to the dealer, scanned and eng coolant sensor came up. He replaced it and only charged me price of part. Now after putting everything back together and starting the car, no heat after letting the car run for 1/2 hour. Took it for a drive and as long as the car was moving I had heat. Once I stopped , it turned ice cold. Went back and he worked on it for a lil bit. Eventually the heat started coming on slowly. He took it out for a test drive,when he came back the heat was almost back to normal. He told me I have to drive the car for 45 mins to an hr and it should be ok.
Now my question is , is this normal? Reason I ask is ive done work on cars before and never went thru so much priming an running the car for any period of time just to get the heat back, especially for just changing a sensor ! ! !

Prospeeder

Thats the sign that the heater core is getting plugged up. The air gets stuck in them and is very difficult to expel. Try flushing it both ways with a hose and driving it. Get a few high rpm pulls to really get the water moving and the air pushed out.