The loose plate will really kill water flow under any kind of pressure as it sucks in air. The plate needs to be "flat" and the "0" ring must be seated. If any air is getting sucked in anywhere the system will not function well.
Also take a good look at the impeller as running dry will damage it quickly.
Check for a restriction at the exit fitting on the manifold sa it can gather krap and restrict flow.
Dave Neptune
