Low pressure is a pool term that is often used to describe weak jets as well as a low PSI reading on the filter’s pressure gauge. High PSI readings will also cause low water pressure. A low or high PSI reading is anything outside the normal operating pressure of the filter. Weak jets, air bubbles, slow pool cleaners and weak water features are obvious signs of low pressure. This guide addresses the common causes of low water pressure in a pool.
First, a short discussion on how a pool system works. The piping in a pool has two sides: the suction side that is before the pump and a pressure side that is after the pump. The pump creates a vacuum that sucks water from the pool and then pushes it back into the pool through a filter. A leak in the suction side will cause air to be sucked into the system. A leak on the pressure side will cause water to spray. If you have a blockage in the suction side of the pump, the blockage will restrict the amount of water to the pump that will result in low pressure. A blockage in the pressure side, like a dirty filter, will have the opposite effect and will cause the pressure to go up. Here are the common causes for low pressure - the easiest to fix is explained first.
CLOGGED SKIMMER BASKET (Low PSI) - If your skimmer basket is full of debris, you are effectively shutting off the pipe between the skimmer and the pump. Generally, this will reduce the flow of water to the pump. If the pump has less water entering it, it is moving less water out. This means the pump is doing less work that in turn will reduce water pressure.
Solution: Clean your skimmer basket by removing any debris.
CLOGGED FILTER (High PSI) - Again, if water can't get through a clogged filter, you will have less water flowing out of the filter. Incidentally, this will increase the water pressure in the filter signaling that it is time to clean the filter.
Solution: Wash your cartridge filter. Periodically soak the filter overnight in a TSP solution to get the grease and gunk out of the folds. Grease is produced by suntan lotion, sebum (oils secreted by the human body) and pine tree needles. Then soak the cartridge in a weak solution of muriatic acid (10:1) to get the minerals out of the folds. Use the TSP before the acid or the gunk will set up in the folds. For sand filters you will need to backwash as required. Change the sand every five to seven years. In between changes, if sand has caked on top, take one to two inches off at the top and replace it with new sand.
CLOGGED IMPELLER (Low PSI) - This problem is often overlooked. If the impeller becomes clogged with debris, water can't rotate out the sides of the impeller. This decreases suction which reduces water flow through the pump.
Solution: Clean out the impeller. See our guide on "How To Clean Out a Pool Pump Impeller".
SUCTION LEAK AT PUMP (Low PSI) - The pump lid o-ring, pump intake fitting, and drain plugs are common areas to draw in air. A suction leak in the suction side of the pump can cause a number of problems. If it's large enough, too much air will be sucked into the system, and the pump will lose prime. If it's smaller, air will be sucked in through the pump and start to collect at the top of the filter tank. After some time (sometimes a few hours) air pressure at the top of the tank will create enough back pressure to reduce the flow of water significantly. When the pump is shut off, this back pressure will cause the water in the suction pipe to surge back and sometimes create a column of water up though the skimmer.
Solution: Find the suction leak and close it. See our guide on "How to Identify and Correct Air Leaks".
SUCTION LEAK AT DIVERTER VALVE (Low PSI) - The diverter valves in front of the pump control the flow of water from the skimmer, main drain, and vac lines. They also have seals in them that can go bad and allow air to enter the system. Again, air will cause the water pressure to drop and will lead to the pump losing prime.
CLOGGED PIPE GOING TO THE PUMP (Low PSI) - A clogged pipe from the skimmer, suction line or main drain reduces the amount of water to the pump which can reduce water flow to the pump and create low water pressure out the return lines.
Solution: Push a stiff wire down the skimmer or suction ports to see if you have a clog near the entrance. If there are no clogs there, you may have to get a pool professional to come in to check your pool pipes.
TOO MANY FEATURES OPENED - The pump is only designed to move so many GPM. Too many water features are like too many hoses on a sprinkler system. The first one has great pressure. Subsequent hoses will reduce the water pressure.
Solution: Alternate which features are turned on or replace the motor in your pump with a larger one. Make sure your existing filter will support the larger pump. You may also have to replace it.
PUMP IS TOO SMALL - If your pump's size was calculated for you initial pool system and you have added more equipment onto that system, you may have exceeded the pump's capability to supply the GPM that is now required. Also, if you have moved your pump significantly further away from the pool, which required more pipe, you may have increased water resistance in the pipes that exceeds the pump's capability.
Solution: Replace the motor in your pump. Note you may also have to increase the size of your filter if it won't handle the increased GPM water flow. See our guide on "How To Replace the Motor on Your Pool Pump".
BAD PRESSURE GAUGE - Pressure gauges on top of the filter do go bad. Your apparent low-pressure reading may be due to a faulty gauge.
Solution: Replace the pressure gauge. See our guide on "How To Replace a Pool Filter Pressure Gauge on a Cartridge Filter".