Pool Pump Loses Prime When Turned Off

If you are wondering ‘why your pool pump loses prime when turned off’, you are not alone. It’s a common issue that many pool owners face and can be quite perplexing. Therefore, I will help you learn five reasons behind this problem and share some personal experiences to make it more relatable. 

In this article, you will find a solution for the pool pump losing its prime when turned off. But before I tell you all this, you must understand why my pool pump loses its prime when turned off.

3 Reasons Why Your Pool Pump Loses Prime When Turned Off? (With Solutions & Prevention Tips)

3 Reasons Why Your Pool Pump Loses Prime When Turned Off?

Insufficient Water Level in the Pool

First of all, you must maintain an adequate water level for the smooth operation of your pool. If insufficient water is in your pool, the pump will fail to effectively circulate and filter the full water, leading to an epic loss of prime when turned off. Below I’m mentioning some of the reasons behind certain water loss in your pool, leading to a loss of prime when turned off.


One of the primary reasons behind low water levels in a pool tends to be evaporation. According to a national renewable energy laboratory study, swimming pools are losing an average of about 0.625 inches of water per week due to evaporation, especially on hot sunny days when the sun is scorching above.


A pool leak is another potential cause of a sudden decrease in water level. You should know that even a small leak can result in significant water loss over time. Therefore, make sure to do it through an inspection of your pool for any visible leaks or signs of water seepage. Also, fix the leaks to maintain the water level and prevent the pump from losing its prime when turned off.

Backwash Water Loss

During maintenance, you also need to backwash the filter & laterals where a substantial amount of water is discharged. Therefore, replenishing the water adequately will further lead to a higher water level in the pool. Therefore, monitor the backwashing process and add water to compensate for the loss. To know more, read: Can You Backwash a Pool Too Much?

Air Leakage in the System

Another reason your pool pump loses its prime when turned off could be early within its system. Air leaks within the pool pump system can also cause significant loss of prime in the filter. Therefore, exploring where air can enter will help you find the solution and prevent it.

Pump Lid or O-ring

The pump lid and its o-ring are critical to maintaining a sealed system. However, you should know that the o-ring may become worn or damaged over time, resulting in sudden air leakage. 

Therefore, it is important that you also pay attention to the inspection of the o-ring and ensure it is clean & properly lubricated for a secure fit. If you find any signs of damage or wear on the or-ring or pump lid, replace it as necessary.

Plumbing Connections

Another common cause of air leaks tends to be loose plumbing connections or faulty ones. Faulty plumbing connections can introduce air quickly into the system, disturbing other functions. 

Therefore, you must inspect all the connections, including pipes, bags, and fittings, for any signs of leaks or loose connections. If you find any leak or loose connection, tighten them to prevent air leakages.

Valves and Seals

Damaged or worn-out valves & seals are also capable of allowing water to enter the system and disrupt pump function. Therefore, check the valve and seal for any visual signs of wear & damage like cracks or tears. If you think that replacement is necessary, do it to maintain a tight seal.

Clogged or Dirty Pool Pump Strainer Basket

Clogged or Dirty Pool Pump Strainer Basket

Another potential cause of your pool filter losing its prime when turned off could be clogged or dirty pool pump strainer baskets. Clogged pump strainer baskets can impede water flow and further lead to a loss of prime. Therefore, below, you will explore some causes and solutions to maintain a clean strainer basket.

Debris from the Pool

It’s not uncommon for leaves, grass, insects, and other debris to accumulate in the strainer basket and obstruct the water flow. This is why we expand as experienced pool owners; we highly advise regularly cleaning the strainer basket by removing any debribuildupld-up to ensure proper water circulation.

Algae Growth

Another potential cause of strainer basket reduced efficiency can be algae growth. Inside a pool system, algae can also grow inside the strainer basket. Therefore, make sure to use appropriate algaecide & follow a regular maintenance routine to control algae growth. This will keep the strainer basket clean and prevent any potential blockages.

Filter System Issues

Maybe your pool filter is malfunctioning, or it is very dirty, contributing to a clogged strainer basket. If this is the case, make sure to clean the pool filter regularly or replace them if required following the manufacturing recommendation. 

It is important to have a clean & properly functioning filter to enhance the overall performance of the pool system and prevent the prime from losing when turned. It is best if you remove the debris from the strainer basket on a regular basis while using appropriate algaecides to prevent algae growth.

Blocked or Obstructed Impeller

If your pool pump system is not able to generate the necessary pressure required to circulate the water, there must be a blocked or obstructed impeller. A blocked or obstructed impeller will not only disrupt the flow but also cause a sudden loss of prime. Below I am mentioning some of the potential common causes and solutions for this kind of issue.

Debris Accumulation

First, inspect the impeller and check out any debris accumulation like leaves, twigs, or small objects obstructing its rotation. If there is any debris accumulated, it will prevent the pump from effectively moving the water, putting strain on the prime and letting it come off even when the pump is turned off. Therefore never mind also regularly inspecting and cleaning the impeller to remove debris.


The impeller movement may be restricted due to build-up of calcium. You should know that calcium build commonly called scaling, can occur on the impeller due to the mineral content in the pool water. Therefore, I recommend always using an appropriate cleaning agent to remove calcium deposits effectively and ensure the impeller functions properly.

Mechanical Issues

Sometimes mechanical issues like worn-out or damaged impellers contribute to overall blockage. Therefore, if you find any damage sign on the impeller or suspect a mechanical problem with the impeller, make sure to seek advice & consultation from a professional pool technician who is an expert in assessing and repairing this issue.

Problems with the Check Valve

Sometimes your pool pump loses its prime when turned off due to a problem with the check valve. Since the check valve is designed to prevent water from flowing back into the pool when the pump is turned on, any issue with it will further lead Pool Pump Losing Prime Overnight. Therefore, understanding the common problem and their solution will help keep the pool pump filter from losing its prime.

Stuck Valve

You should know that check valves are also known to become stuck in the closed position obstructing water flow if it is broken or not lubricated properly. This will further prevent the pool pump from maintaining its prime & functioning properly. Therefore, I recommend that you regularly inspect & lubricate the check valve to ensure smooth operations.

Damaged Valve

Sometimes damaged check valves like cracked or broken components also cause this kind of water flow problems & loss of prime. Therefore, I advise you to take some movement & watch out for any visible signs of damage. If you think the check valve requires replacement to restore proper function and prevent prime loss, make sure to do it.

Improper Installation

Lastly, incorrect check valve installation will also create problems like impeding water flow and more serious issues. Therefore, ensure that you check the valve is correctly installed and aligned with the flow of water. Also, make sure to make any necessary adjustments to optimize its performance.


After reading this article, I hope you know why your pool pump loses its prime when turned off. I’ve given my full effort to helping you find an appropriate understanding of all the reasons to take your first step toward finding the right solution. 

If you follow all these tips mentioned in this article and the issue of prime loss still persists, never mind consulting with a professional. However, addressing some of the most common issues mentioned in this article, like insufficient water level, air leakage, clogged strainer basket, block impeller, as well as problems with the check valve, can help you maintain a properly functioning pool pump system with its prime on it. 

However, also pay attention to the regular inspection, maintenance, & cleanliness of your pool equipment to further ensure optical performance as well as enjoy a well-circulated & clean pool throughout the year. 

Always remember that maintaining a well-maintained pool not only provides enjoyment but also contributes towards the longevity and sustainability of your pool system. If you find the article helpful, then consider sharing it. 

Your share is not only going to help people learn why the pool pump loses prime when turned off but also what are the necessary steps they need to take towards finding the right solution. Do check my other helpful guide on pool care & maintenance. See you in the next post, till then, take care & goodbye.