Though air can get in through the valve stem, it would do it regardless as the what position the handle was turned, so it sounds like the low suction line is the culprit. What I would do is turn off the skimmer line and slowly but continuously dribble water on any suspect connection and watch to see if the bubbles lessen or stop, if they do, you've found a leak. I would check any threaded connection first.
Bookmarks