Nissan Altima: 02 altima heating problem

I have the same problem with my car and nissan said that it might be an air
pocket, but then I got there and they put it under pressure and said its
leaking I need a new radiator. I dont understand that because the fluid
never has leaked on the ground and its always full. I put a new thermostat
in it and its still does it. It really is aggrevating to me. Last year they
had to replace the switch on the heat knob because the knob was only
turning to med heat but I cant imagine that happening again. Let me know
what you came up with.

My 02 altima has the same problem with the heat not working while idling.
I have had it in the shop 4 times and they keep replacing things and it is
not fixing the problem. Has anyone had this problem actually fixed?