I am having a similar problem with a Hayward Super Pump 1.5 HP and a Hayward Sand Filter. The system was installed four years ago and the problem occurs during the first month or so or each season since installation. However, when the pump is turned off while the filter valve is in the filter selection, the sand filter drains quickly and the pump basket drains about half way. I typically have to prime it a couple of times before it finally catches when starting back up, but I also continue to have a small to moderate amount of air bubbles. I have replaced the O-Ring on the pump each year and this year, suspecting the cover to the pump might be faulty (slight ejection of water out between cover and pump basket when pump shut off), I replaced the cover on the pump basket as well. All was well for a week and now the problem returns. I have suspected the possibility that the rings in the filter valve might be the culprit as well - is that a likely possibility. I should replace the sand, so I could do all this at one time.
Thanks for any help!!