Let’s rule out the most dangerous situation of high filter PSI which is a blockage in the line. This is probably the rarest but can be the deadliest as your filter tank could explode. Typically, it is something after your heater, maybe a broken check valve or debris lodged in your salt cell. On even rarer occasions I have had customers deadhead their pool return by over-rotating the Jandy Valve past the safety notches. Typically a filter that has a blockage will have the PSI spike rapidly and the skimmer will have poor flow.
The most obvious reason for the high PSI is that the filter is dirty. Simply cleaning the filter or backwashing it if you have a D.E. Or Sand Filter will usually lower the PSI down to the acceptable range. The clean starting filter PSI will vary from filter to filter, some hover around 10-15 PSI but many cartridge filters start at 20 PSI. The best way to know in your case is to clean the filter and then mark on the gauge the clean PSI for your particular filter.
A general rule of thumb is that if the PSI goes up by 10, if it is at 15 and goes up to 25, then cleaning or backwashing is due. This is the best way to lower down high filter pressure and get the pool circulating again.
After cleaning the filter or backwashing it the filter pressure should drop. If it goes back up within a day or week there could be a few reasons for this. One, the grids or cartridges are worn out and need to be replaced. If you have a Sand Filter the sand could be really dirty and you will need to clean it or replace it. Also, if the pool was recently green or cloudy, the filter could be getting filled up quickly with organic matter. Cleaning the filter again usually will solve the issue. If the D.E. Filter grids have a tear or the top manifold is cracked, the filter pressure can rise rapidly after cleaning.
If you have a Return Side cleaner connected to your pool like a Polaris 360, the PSI may rise while it is connected due to the backpressure created by closing off a return line and by the cleaners connection itself. This is normal and nothing to be concerned about. The pressure may also be higher by as much as 10 PSI when you switch the valves to spa mode. The backpressure created by the spa jets will cause the filter pressure to rise. A water feature may also cause the filter PSI to rise.
So these are basically the reasons why your pool filter pressure will rise.
If you have low pool filter pressure a number of things may also cause this. The most common reason is some debris is stuck in the pool impeller, restricting it and causing the pump to pull less water. A suction leak like a worn pump lid o-ring will also cause low filter pressure. A problem with the pump's diffuser can also cause this.
Some obvious causes are also a clogged pool pump basket, a clogged skimmer basket and low water in the pool. Too much suction at the side port towards a suction side cleaner can also cause lower pool filter pressure. A clogged inlet line can also be the cause of low filter pressure. If you have a variable speed pump and you are running it at or below 1400 RPM, the filter pressure PSI will also read low.
A broken filter gauge can also create a false PSI reading – either too high or too low, so make sure the gauge is in good working order. They are easy to change and it will only take you a couple of minutes to do it.
I mention that a flow gauge like the FlowVis would be a good investment and if you really want to get the best idea of your pool's actual flow, I suggest you install one. That way no matter what the PSI on the gauge, you can see from the flow meter how much water is actually flowing into the pool. This is the best way to monitor your pool's actual flow.
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