Diagnosing and Fixing Pool Filter Pressure Problems

The pool filter pressure gauge is one of the most important parts of your pool filtration system. While it really doesn’t -do- anything for your pool, it plays a vital role by telling you how all of the other parts are doing at a glance.

Trick question! There is no normal pool filter pressure as every pool’s “normal” reading will depend on a variety of factors like the size of your pool pump, the size and type of your pool filter, the number of skimmer boxes and inlets you have, and even the size of your pool. The only way to determine what your “normal” pool filter pressure is to record it when your filter elements are at their cleanest: after backwashing your sand filter or cleaning out your filter cartridge.

Note: Every time you change a component in your pool like the filter itself or your pool pump, you’ll need to re-record your baseline filter pressure reading as any change in configuration will affect what your pool’s “normal” reading will be.

Once you have your baseline pressure, we can now start to talk about what the possible issues are when the pressure reading strays from the normal and what we can do to relieve it.

If your pressure gauge reads lower than normal, it is almost guaranteed that you have a problem within the pump itself or before the pump, and never after the pump itself. The reason for this is that anything after the pump will be pressurised by the vortex created by your pool pump’s impeller so a low pressure problem cannot be caused by anything after the pump. Now that that’s out of the way, here are some things that we need to check when we run across low pressure problems.

• Clogged Pump and Skimmer Baskets - This is the most common cause of low pressure problems and thankfully the easiest to remedy. Simply clean out your pump or skimmer baskets to restore the flow of water and you should be good to go.
• Low water level - A low water level can also cause low pressure problems, if there isn’t enough water entering your intakes or skimmer boxes then there won’t be enough water flow to create the right pressure levels and could introduce air into the system. To prevent this, always check your pool water levels and top up whenever necessary. You can also automate this by getting an automatic pool water levelling device that fills up the water to optimal levels whenever it drops.

• Clogged Skimmer lines - You’ll need something like a drain king bladder-type hose jet to blow out whatever it is that’s clogging up your skimmer lines.

• Clogged or Damaged Pool Pump Impeller - If you’ve read our guide to how pool pumps work, it explains there how the pump, more specifically the impeller, creates the suction and pressure for your system. If the lines going to your pump are clear, then it could be a problem with your impeller.
• A leak somewhere before the pump - Another cause for low filter pressure (or even a fluctuating one) is a leak before the pump. This is also a cause for your pump surging or pulsing.
• Broken pressure gauge - If everything else fails, be sure to check and replace your pressure gauge before you start ripping up pipes trying to figure out if there’s a blockage somewhere. Pressure gauges are fairly cheap and they’re known to fail time and again, this is why we recommend to always have a spare available so you can check on the fly.

• Leaky 3-way valves or multiports - This is also another reason for low pressure. Check if your 3-way valve after the pump or if your multiport is properly channeling water and not leaking. If your valve is leaking then the only way to fix it is to replace it.

If everything is working normally then a high pressure reading shouldn’t be a cause for alarm or worry. Simply clean out your filter cartridge or backwash your sand filter and it should go back down to normal levels. Now if the pressure reading doesn’t go down after cleaning your filter elements, then there could be a number of reasons that could be causing that:

• Closed or Partially closed return valves - This can cause wild spikes in pressure readings so check and fully open your return valves if you’re using them.
• Overtly dirty chlorinators - If you’re using a salt water chlorinator, an excess of calcium or lime deposits could cause high pressure levels (and improper chlorination!) so it’s one of the first things to check if you have high pressure readings on your pool filter.
• Air inside your filters - having air inside of your filters can cause high pressure readings, this is an easy fix, simply open up your air bleed valves until water starts to come out and then close it up. The pressure should be relieved and be normalized. If this is the cause for the high pressure reading then it’s also recommended to check your pumps for leaks afterwards to determine the reason why air got into your filters in the first place.
• Oversized pump or undersized filter - If you have high pressure problems immediately after replacing your pool pump or filter then it can be because your pump is oversized or your filter is undersized. There’s no easy fix to this except to either decrease the pump capacity or increase the filter capacity, our recommendation is to increase the filter capacity because you can never go wrong with an oversized filter but an undersized pump can cause problems as well. But if you have a new filter and replacing it seems like a waste, you can also opt to replace your pump with an ECO pump or variable speed pump so you can run it at lower speed to compensate.

This is a problem that isn’t actually a problem. If you’ve seen recommendations around the internet, they will usually recommend that you give your sand filter a backwash every few weeks or your filter cartridge a good cleaning when the pressure rises. But what if it has been more than a month and the pressure still hasn’t risen significantly for you to consider cleaning the filter elements? Well, this means that your filter still isn’t dirty and is probably oversized. This isn’t anything to worry about. In fact, this is good. This means that you’ll have more time in between cleaning cycles and you’ll use up less water! Remember what we said about oversizing your filters? This is what we meant by you can never go wrong with an oversized filter.

Zero pressure can be caused by two things. The first one, the most obvious is your pressure gauge being broken and a replacement is in order. The next reason, while it may sound silly, is probably a valve in the wrong position. Zero pressure means that there’s nothing going on inside of your filter, so simply check if the valves leading to your filter are in the correct positions. If everything seems to be running correctly, pump is okay, water flow and everything, then give your pressure gauge a few taps, it could just be stuck.

We hope that we’ve relieved some of the pressure (pun intended!) off of your shoulders when dealing with pool filter pressure problems.