I believe that I have a defective pump in my flow controller. The pump itself is noisy. It does work and I do have flow, but it is making a loud whining sound on some cycles, but not on all cycles. We did have air in the system first which had its own distinct sound and had to have the contractor come out to re-flush the loop. To replace the Grundfos pump, do I need to have the loop re-flushed or can I just replace the pump itself without introducing air to the system?