I have Hayward system, Sand filter, Hayward 1.5 pump. Sand replaced 2 weeks ago. The pump is on and about an hour PSI goes up approx 10 PSI and then very little if no flow. I have back washed and rinsed. I turn on pump again, same issue. If I then turn off the pump for 2 minutes(no back-wash) and then turn it back on, it runs for the approx 1 hour, low PSI and then same issue, (PSI goes up very little flow) I have put it on recycle to test for 1.5 hours, no issues. I have checked seals, re-lubed gaskets etc. I asked a local pool place and they don't know> Help.