Bill,

When I first started running my Renesis I had heating problems similar to yours.  I found out that air could be trapped in the water pump and the impeller would never pump any water because of the air the impeller was spinning in.  I put a spigot on the top of the thermostat housing.  My radiator and engine block have small bleed lines on the high points returning any air to my air/water separator- reservoir tank.  When filling I open the spigot and fill my system.  The filler tank is slightly higher than the spigot.  When full, all the air has been pushed out of the whole system.  This is by design per Al Wick's recommendation.

You should be able to tell if water is flowing by making sure the end tanks of the radiator are both getting hot.  I have a dual pass radiator and have not had any indication that the water flow rate is reduced significantly. Dennis H.