I have a Pentair FNS 36 Plus DE filter for an in ground pool. Last weekend I cleaned the DE and replaced it making sure to lube the O Ring and tap the band connecting the two halves of the filter tank while tightening.
When I restarted the pump I noticed a small trickle of water coming from the back of the band that holds the two halves of the filter together. I also noticed that the pressure gauge on top of the filter was pretty low (~4 psi). I vented the filter tank of all air, waited a few seconds and found there was more air to vent. It seems that water is seeping out and air is seeping in.
I took the filter tank apart and inspected the O Ring - it looked ok - I re-lubed it and reinstalled it and put the band back on. When I restarted the pump I see the exact same behavior - small leak, low pressure, air in the filter tank.
I hope it is just a bad O-Ring but it looks ok to me - is there anything else I should look for before ordering a replacement? I read related threads in this forum and have checked the ORing in the pump basket and have looked for any obstructions - none are obvious. Also of note is that there is good suction at the skimmer so the pump appears to be working well. Thank you for any advice you can give!