If the pump is submerged, check that the supplied NRV is fitted directly to the pump inlet. A floating intake with NRV is not sufficient as the NRV must be connected directly to the pump inlet.

If the pump is surface-mounted the NRV may be fitted at the end of a run of rigid suction pipe.
For horizontal pumps the intake is on the end of the pump and the outlet projects from the body nearer to the rear electrical cover.

For vertical pumps the inlet is the lowest connection and the outlet is the highest.