have you used the heater since you flushed system, when you flush system out you have to turn heater on full to bleed or you air pocket in heater unit under the dash, keep car level when bleeding fill remove bleed bolt from engine and fill radiator till no more air is coming out of bolt hole then put bolt back in while water is coming out, if you left front of car up you will get small air pocket at front of engine as it is made so the bolt is highest point when car is level.