Why is there no heat coming out the vents on your 2003 Mercedes Benz E-320?

If there is no heat coming out of the vents, but there is air coming out on a 2003 Mercedes Benz E-320, check the thermostat to make sure it is not sticking. If this is okay, check the heater core. If the heater core is bad, there will be water on the passenger side floorboard.