with the ignition off, press the "rest" button on your a/c control panel. Then go into the engine bay and feel the circulation pump with your hand......you should feel it operating. If you do then the fault isn't the pump, but it might be the heater valve. If it isn't running then check if it's getting a voltage at the motor (if there's voltage then it's the motor at fault, if not then the fault may lie further up the electrical system.
It pays to do through checks before starting to replace components, it's cheaper and more accurate in the long run.