Overheating, I have changed my water pump, my thermostat, my radiator, head gasket, fans are working

I have changed my water pump, my thermostat, my radiator, head gasket, fans are working. mechanic has completely taken the engine apart and has reassembled and it continues to overheat. mechanic says that there is air in the engine and he needs a special tool to take out the air. he tried to take off the air and he is unable to do so. I have been without a car for a month. people have told me it was a blown head gasket. it's not a blown head gasket. people tell me if the water pump is brand new also was tested that it was good. mechanic seems to be questioning himself. if you were in my position what would you do how would you handle this problem? any advice?