Also posted on outdoor forum. Just looking for some help.

I just cleaned the grids on my Hayward DE filter. Started everything back up and the pump starts to cavitate and the filter housing fills up with air. I've bled the air off for days but it continues to gas up. This same thing happened the last time I cleaned them but never before. I'll describe my troubleshooting below but the last time I gave up and shut the pump off for 4 or 5 days before the pool tech could get here to diagnose. When he arrived we started the pump, bled some air off, and everything ran perfectly fine.

During my first round of troubleshooting I replaced the union on the suction side of the pump. I replaced the pump lid and gasket. I can run water over all the suction piping and the bubbles don't stop. I replaced the gasket on the valve on the suction that differentiates between either the pool or the spa. None of that helped. It was not until what I described above happened before everything worked right again.

I'm back in the same boat and have no idea what fixed it the last time, so I have no idea what to do this time. I'm in south east Texas so can't afford to leave the pump down for days without building algae, which means I'll have to open up and clean the grids again after filtering all the algae.

Anyone have any thoughts or ideas?

Thanks.

with the lid off, start filling up the pump (and the feed pipe) with water. Fill it up as much as you can and then put the lid on and start the pump to see if that gives enough prime to get it going. I suspect you have a crack or some kind of leak letting in air, but if you can get it primed and flowing water you might might be able to see where the crack is (if there is one).