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If the system was full, then warm motor up and check the 2 heater hoses, are they hot? Where on the car do you see the leak? When you checked the coolent level, did you check it in the rad. or the bottle or both? Let me know and I will try to help you find your problem.
When I checked the fluid, I checked it in the re-fill container for the coolant. The leak was coming from underneath the car on the passenger side. I think it was coming from the water pump.
Check the rad. see if it is low there. If you are leaking coolent from the water pump, The rad. will get low, causing your heat not to work.