Filter pressure drops instead of rising after running?
- Thread starter syedsam
- Start date
John Faulkner
Member
I’d also double-check the gauge itself. Sometimes a sticky gauge gives misleading drops. Swap it out for a cheap new one before diving into major repairs.
Kevin Marsh
Member
I’ve actually run into something similar once. A steady pressure drop usually points to something disrupting the pump’s ability to maintain consistent flow. Air leaks, like Manikshaw mentioned, are a common cause, but another thing to check is whether your pump basket or impeller is getting partially clogged and then clearing itself as debris shifts around.
That can cause pressure to dip instead of climb. Also, make sure the water level in your pool is high enough and the skimmer weir isn’t sticking, because low water level can let the pump draw in a bit of air over time. If those all check out, I’d also take a look at the gauge itself, sometimes a failing gauge gives odd readings and makes you chase a problem that isn’t really there.
That can cause pressure to dip instead of climb. Also, make sure the water level in your pool is high enough and the skimmer weir isn’t sticking, because low water level can let the pump draw in a bit of air over time. If those all check out, I’d also take a look at the gauge itself, sometimes a failing gauge gives odd readings and makes you chase a problem that isn’t really there.
Lily Allen
Member
I’ve seen the same drop in pressure too! It’s usually a sign of a blockage somewhere, like air entering the pump or the sand channels being blocked. I once swapped the gauge first to see if that was the issue, then checked the pump basket and impeller for debris. It helped! Anyone else check the pump basket as a first step?
Henry Thompson
Member
I had almost the same head-scratcher a while back, and it turned out to be the multi-port valve. The spider gasket inside mine had worn down, so the water was slipping past in weird ways, and the gauge would drop instead of climb.
At first, I thought it was air leaks or the sand, but once I replaced the gasket, the pressure readings returned to normal. If you’ve ruled out the easy stuff like the basket or gauge, it might be worth giving the valve a close look.
At first, I thought it was air leaks or the sand, but once I replaced the gasket, the pressure readings returned to normal. If you’ve ruled out the easy stuff like the basket or gauge, it might be worth giving the valve a close look.
Benjamin Tate
Member
Yeah, that backwards pressure trend usually means resistance in the system is decreasing while it runs, not increasing like it would with a dirty filter. One thing I don’t see mentioned yet is debris slowly shifting off the sand bed or out of the plumbing once the pump’s been running for a while.
I ran into this after a heavy vacuuming session. Fine junk got pulled into the filter and some of it partially blocked the standpipe or settled unevenly in the sand. When the pump first kicked on, pressure looked normal. After a few hours, the flow paths kind of re-established themselves, channeling formed, and pressure dropped because water found an easier route through the sand. Flow looked “okay” but weaker, exactly like you’re describing.
Another clue is air in the system. Even a tiny suction-side leak can slowly accumulate air in the filter tank. You might not see obvious bubbles at the returns, but the air pocket reduces effective filtration area, which lowers pressure over time. Next time it’s running, crack the filter air relief or bump the pump lid and see if a lot of air releases.
If it were mine, I’d note pressure right after a backwash, then again after 4–6 hours at the same pump speed. If it keeps dropping, I’d deep clean the sand bed with a hose before tearing into anything mechanical. When pressure drops, it’s usually telling you water is taking shortcuts, not that the filter is getting cleaner. Anyone else notice the flow feels different even though the gauge is lower?
I ran into this after a heavy vacuuming session. Fine junk got pulled into the filter and some of it partially blocked the standpipe or settled unevenly in the sand. When the pump first kicked on, pressure looked normal. After a few hours, the flow paths kind of re-established themselves, channeling formed, and pressure dropped because water found an easier route through the sand. Flow looked “okay” but weaker, exactly like you’re describing.
Another clue is air in the system. Even a tiny suction-side leak can slowly accumulate air in the filter tank. You might not see obvious bubbles at the returns, but the air pocket reduces effective filtration area, which lowers pressure over time. Next time it’s running, crack the filter air relief or bump the pump lid and see if a lot of air releases.
If it were mine, I’d note pressure right after a backwash, then again after 4–6 hours at the same pump speed. If it keeps dropping, I’d deep clean the sand bed with a hose before tearing into anything mechanical. When pressure drops, it’s usually telling you water is taking shortcuts, not that the filter is getting cleaner. Anyone else notice the flow feels different even though the gauge is lower?
Brandon Hayes
Member
One other angle that doesn’t always get flagged is temperature and pump efficiency over a longer run.
I chased this once thinking something was seriously wrong because I’d start around 14–15 psi and end up closer to 9 after a few hours. Turned out the pump motor was heating up and the water temp was climbing at the same time. As everything warmed up, the system moved water a little easier, less resistance, so the pressure settled lower even though nothing was actually “fixed.” Flow felt slightly softer but steady, not collapsing.
What tipped me off was that if I shut the pump off for 30 minutes and restarted, pressure jumped right back to the original number, then slowly drifted down again. No air leaks, no sand issues, just normal changes in viscosity and pump performance once things stabilized.
Might be worth checking if the drop is gradual and repeatable like that, especially on hot days or with a pump that’s been running nonstop. If pressure drops smoothly and then plateaus, it’s often physics, not a failure. Anyone else notice theirs reads totally different cold-start vs fully warmed up?
I chased this once thinking something was seriously wrong because I’d start around 14–15 psi and end up closer to 9 after a few hours. Turned out the pump motor was heating up and the water temp was climbing at the same time. As everything warmed up, the system moved water a little easier, less resistance, so the pressure settled lower even though nothing was actually “fixed.” Flow felt slightly softer but steady, not collapsing.
What tipped me off was that if I shut the pump off for 30 minutes and restarted, pressure jumped right back to the original number, then slowly drifted down again. No air leaks, no sand issues, just normal changes in viscosity and pump performance once things stabilized.
Might be worth checking if the drop is gradual and repeatable like that, especially on hot days or with a pump that’s been running nonstop. If pressure drops smoothly and then plateaus, it’s often physics, not a failure. Anyone else notice theirs reads totally different cold-start vs fully warmed up?