Filter pressure goes UP when I backwash?

John Faulkner

John Faulkner

Member
Weirdest thing: I backwashed my sand filter yesterday, and instead of the pressure dropping like normal, it actually climbed higher than before. Pool looks okay but the gauge is reading almost in the red. Did I mess something up, or is my filter cursed?
 
Could also be a bad gauge giving you nonsense readings. If water flow looks normal at the returns, swap out the gauge first before panicking.
 
That usually means the sand bed might have compacted or channeling is happening. When you backwashed, debris shifted and clogged tighter instead of loosening.
 
If neither of those, check if you accidentally set it to recirculate or rinse incorrectly. Mis-valving can cause strange pressure behavior.
 
I’ve had this happen when debris got packed in tighter during backwashing. After backwashing, I found the sand bed had shifted and clogged up a bit instead of loosening. I did a quick rinse, and the pressure settled back down. Anyone else have the sand bed shift after backwashing?
 
This usually happens when the sand bed has compacted or channeled. When you backwashed, debris shifted and clogged tighter instead of loosening.
 
If the pressure goes up after a backwash, I check three things first: the multiport valve position (make sure you are actually back on FILTER after BACKWASH and you did a RINSE), the pressure gauge itself (they can fail), and whether the sand bed is compacted or channeling so debris actually packs in tighter. If the flow at the returns still looks normal, I usually try another backwash and a longer rinse. If it is still near the red, I shut it down and check the valve and gauge before I keep running it.
 
Haha, it is not “cursed,” but this can happen. If your pressure climbs after a backwash and is almost in the red, it is usually one of these: the rinse step was too short, the multiport valve did not fully seat back on “Filter,” the pressure gauge is starting to lie, or the sand bed is compacted/channeling so the backwash shifted junk around and actually clogged things tighter.
What I would do is shut the pump off, make sure you press the multiport handle down fully when you switch positions, then redo the backwash until the water looks cleaner and rinse for 20 to 30 seconds before going back to Filter. After that, check your return flow, if flow feels normal but the gauge still looks crazy, the gauge is probably the problem. But if flow is weak and pressure stays high, that points to the sand/filter needing a deeper clean or a closer inspection.
 
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