I am having the same problem. The pool seemed to be fine just the other day. We re-plumbed it this spring. Now, when we turn on the filter, it primes and pulsates (pretty decent water flow) but the air with occassional water spurts out the air valve when we open it. I do hear a hissing sound coming from our push pull backwash valve. It is very hard to open and close and has been for some years. Could this cause a problem. I feel like water is suctioning into the pump but then isn't making it to the filter. The only valve that I know of between these two points is the one I mentioned (backwash valve). The pressure reads 0 to less than 5 (pulsates). I tried taking an air compressor to blow out anything that may have been stuck, but it didn't dislodge anything this time. We did fix a leak today that was before the valve (backwash). I have no idea what it could be. I did spray all piping etc with soap water and that is how the leak above was found. No other leaks are detected. The O ring for the pump motor is new, as are all the seals. At least, new this Spring. Any info would be greatly appreciated. I did take water in for a sample today because it seemed a bit cloudy but was told all is well just to run pump longer. Can't run it now.
forgot to mention the air is coming out where the backwash valve gushes water (took of the hose to find leak). I did backwash and water came out, good amt, but not the typical river rush. No water is coming out when on filter just air noise and I can feel it.