Ford Repair: coolant flow, water pump impeller, 1963 ford galaxie

Question
Dennis, Thanks for the advice. When I checked the system before asking the question the port in the manifold flowed freely. However, the water pump may be the problem. It is a rebuilt unit I installed  one year ago, less than 500 miles since then. The car ran a little on the warm side before and after changing the pump. Is there a way to check the flow other than looking in the radiator? I can see water movement in the radiator but not very much movement.If I change the water pump again, what should I look for in the impeller? Jim-------------------------
Followup To
Question -
1963 Ford Galaxie, coolant doesn't flow to the heater core. I replaced the heater core and flushed the entire system,new thermostat, old radiator. Coolant flows thru the rest of the system but doesn't flow thru the heater core. The new core isn't blocked as I poured water in one hose and it came out the other. Why won't it flow and how do I repair this problem? Or, where can I find an answer? Thanks in advance for any help you can give. Jim
Answer -
Only two things I can think of, Jim, either the port on the intake manifold is plugged or the water pump impeller is worn and not pushing the fluid.  

Answer
If the system was rusty or dirty the corrosive effects would eat away at the water pump impeller. I remember seeing on e of these with the impeller loose on the shaft, thereby not spinning at the correct speed. If nothing comes out the heater port I would suspect something like this, or a gasket installed incorrectly. Has any engine work been done recently?