I have a PB4 Booster Pump that suddenly doesn't seem to pump water through to the Polaris sweeper. I had opened the Hayward main pump to remove debris from the basket. Afterwards, I let air out of the filter, recapped the Hayward, then started it up again. It finally primed, but then when I went to turn on the booster pump, it just gave a whining sound like it was running but not pushing water. If I unscrew the polaris from the pool wall, some bubbles are visible coming out of the piping, but they just keep coming. My internet searches have been fruitless, and I'm not having any luck getting this pump to prime again so that I can run my Polaris. Any ideas about what I'm doing wrong?