That's a good package.......but the FWC will last a long time....
I think you definitely have a loop that locks it up. I think there's a pretty easy fix for it though.....you have a hose from the heatexchanger going to each of the exhaust elbows. If you put a Tee in one of them and put a valve on it you can open the valve to bleed the air and the raw water will flow in up to the water line level which I think should be enough to prime the pump. I would make sure the valve is ablove the water line....and it doesn't need to be a very big valve since its only going to bleed air.