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Pool Pump Won’t Prime? Here’s Why (+ How To Fix)

Your pool pump needs to prime to keep the water flowing and prevent the motor from overheating. An unprimed motor typically has plumbing issues, but there are many other potential causes.

A pool pump that won’t prime has one of these issues:

  1. Too much air in the plumbing
  2. Warped pump components
  3. Not enough water in the pool
  4. Demanding pool vacuums
  5. Skimmer clogs and blockages
  6. Broken PVC Plumbing
  7. Debris in the equipment pad 
  8. Unsealed lids and unions

In this post, I’ll discuss why your swimming pool’s pump won’t prime and why it needs to be repaired immediately. I’ll also explain the solution for each problem to help you fix your pump without hiring a pool technician (aside from two issues that require professionals).

1. Too Much Air in the System

Air rushing into a pool pump will prevent it from priming. Here are the most common ways that air can flow into the pump:

  • Loose, broken, or dry O-rings don’t create a strong, secure seal.
  • Plumbing issues, including cracks and porous glue let water flow out of the pipes.
  • If the lids aren’t tight on the pump or filter, air can get inside.

How To Fix

Having air in your pool equipment pad can wreak havoc on the system. Here’s what you should do:

  1. Turn off the pump and inspect every O-ring and gasket. If they have cracks or are warped, they need to be replaced. You can also use Lube Tube O-ring Lubricant to prevent dryness, cracking, and other issues. Each bottle contains enough of the solution to last several swimming seasons.
  2. Locate and repair all cracks in the plumbing. Long, UV-exposed pipes, elbows, and unions are very likely to wear down over time. If you spot a crack, it needs to be cut out with a PVC saw and replaced. Dry the new and old pipes, glue a coupling, and use it to connect the exposed portions.
  3. Tighten every lid and union on the equipment pad. Check the pump, filter, heater, and all other pieces of equipment for your swimming pool. Don’t forget to tighten your swimming pool vacuum hoses, too! Air can leak into the unions between each hose segment.

2. Warped Pump Components

Excessive sunlight, failure to run the pump, and overheating can warp pool parts. If your pump won’t prime, it might be due to warped or misaligned lids, unions, O-rings, and plumbing.

Check each of the unions before and after every piece of equipment. Look for bent or warped plumbing because it lets water flow into the gaps.

How To Fix

Unfortunately, warped pump parts can’t be repaired; They have to be replaced. Swim University shows the sun’s UV rays, constant usage, and long-term operation can wear down a pool pump.

It can also take a toll on the heater and filter, so those might also need to be replaced if they’re inviting air into the system.

The good news is that you can replace each part before getting a new pump. For example, if the lid is broken or warped, all you have to do is get a new lid from the manufacturer.

All pool pump parts should come directly from the company rather than a generic brand. These components are specific to the make and model, so they can’t be substituted or replicated.

3. Not Enough Water in the Pool

If there’s not enough water in the pool, your pump will pull air into the basket, motor, and filter. A lack of water can be caused by evaporation and leaks.

It’s essential to keep the pool water above the highest inlet at all times. When the water moves from swimming and splashing, it can pull air into any exposed inlet.

How To Fix

If your swimming pool doesn’t have enough water, we suggest following these two tips:

  • Get a swimming pool cover to prevent long-term evaporation. The Sun2Solar Pool Solar Cover stops the water from evaporating, which stops most priming issues. This solar cover also keeps your swimming pool a few degrees warmer.
  • Look for leaks in the plumbing, unions, and anywhere else the water can leak out. If water is leaking, then air is entering the system. Leaks are frustrating because they’re often difficult to detect. If you think there’s an underground leak, it’s best to hire a professional with a warranty.

4. Demanding Pool Vacuums

Some pool vacuums use electricity, while others require suction from the pool pump. If your vacuum uses the pump’s suction, you’ll need to increase the RPMs.

Without enough RPMs, the suction will be weak and won’t prime the pump. Furthermore, the vacuum hose can push upward and suck air into the line.

How To Fix

Pool vacuums demand more RPMs, so it’s important to know if your pump can handle the pressure increase. You can get a booster pump if you have a pressure-side pool vacuum.

I recommend the Polaris PB4-60 Booster Pump, as it provides enough pressure to propel your pool vacuum without taxing your main pool pump.

Not only does it make your vacuum much more efficient and effective, but it also increases your pump’s longevity. You can run your main pump without worrying about the vacuum ruining its prime or suction.

5. Skimmer Clogs and Blockages

Skimmers are prone to clogs because they prevent large debris from entering the pump. If the debris flow is too much, the skimmer’s gate can jam, slowing the water and stopping the prime.

When the water can’t enter the pump’s inlet, it drops the pressure immediately. Wear and tear, corrosion, and chipped hinges can jam the gate.

How To Fix

I suggest cleaning your skimmer basket as often as possible. All of the leaves, twigs, hair, and other debris that fall into your pool goes to the basket.

This debris clogs and breaks the basket if it’s unchecked. Most pool owners should clean the basket every two to three days.

If the skimmer gate is blocked or jammed, check the hinges. These hinges can get brittle and dry in their slots. They need to be replaced once they’re too brittle.

Much like all other swimming pool parts, you need the exact measurements to get the correct gate. Otherwise, it won’t fit.

6. Broken PVC Plumbing

If any of the pipes in the plumbing are broken, cracked, or leaking, your pump will have a tough time priming. In fact, large cracks will stop the prime, preventing it from starting at all.

Your pump will roar and pull air, frying the motor. Tree roots, direct sunlight, poor chemical maintenance, and many other factors can contribute to broken plumbing.

How To Fix

PVC plumbing needs to be repaired as quickly as possible to prevent further (and more expensive) damage. Here’s what we recommend:

  1. Use a PVC saw to cut the broken portion.
  2. Dry both sides of the exposed pipes.
  3. Cover the first inch of both exposed portions of PVC, then glue the inside of a PVC coupling and slide it over the glued, exposed pipes.
  4. Hold the pipes for 30 seconds to let the PVC glue dry.

If you’ve never repaired PVC pipes, I highly recommend hiring an experienced swimming pool technician. It’s not an easy process, and mistakes can lead to costlier repairs down the road.

7. Debris in the Equipment Pad

Most pool equipment pads consist of a pump and a filter, but there are many other pieces of equipment that you can add. For example, there are salt cells, booster pumps, heaters, solar panels, and several valves on some pads.

Trapped debris in any of these areas can limit the water flow and trap pockets of air in the line, stopping it from priming.

How To Fix

Follow this quick step-by-step process:

  1. Turn off the pump to stop the water movement.
  2. Remove the lid from the pump, filter, and salt cell (if you have one).
  3. Clean the filter cartridges or backwash the DE or sand, depending on which kind of pool filter you have.
  4. Remove all of the debris from the pump basket.
  5. Seal every union and lid, then turn on the pump.

If your pool still has pressure issues or won’t prime from excess debris buildup, you can hire a pool technician to blow the lines with a pressurized tool.

8. Unsealed Lids and Unions

Perhaps one of the most common reasons people can’t prime their pump is because the lid or unions aren’t sealed. This issue usually happens after filling the pump basket, removing debris, or switching the gaskets.

Fortunately, it’s also one of the easiest problems to fix.

How To Fix

Unsealed lids and unions take less than a minute to fix. Simply loosen each portion, align the O-ring or gasket, and tighten the lid or union.

If there’s a leak from one of the unions or lids after you tightened it, you can try one of these tips:

  • Put the previously mentioned O-ring lubricant on every gasket and O-ring to prevent leaks.
  • Replace the unions or lids since they might be cracked.
  • Replaced the O-rings or gaskets since they might be dry, cracked, or warped.

Pool Pump Won’t Prime All the Way? Here’s What To Do

Does it always seem like your pool pump starts priming, then suddenly stops? Maybe the pump almost primes all the way, but it can’t quite finish.

Whatever the issue is, the most common cause is undoubtedly air in the lines.

Pool pumps, filters, heaters, and plumbing need to have nothing other than water flowing through them. Air bubbles will drop the pressure drastically.

If your pump doesn’t prime all the way, check each of the unions and lids for leaks. There’s more than likely a leak somewhere. However, you might’ve not added enough water.

All pool pumps need to be manually primed every time the lid is removed.

  • Turn off the pump.
  • Fill the basket with hose water until it overflows.
  • Tightly secure the lid.
  • Turn on the pump and open the air relief valve on top of the filter to let all of the air out of the system.

Pool Pump Won’t Prime Completely? Here’s What To Do

If your pump won’t prime completely, it’s best to start by opening the air relief valve. This valve is located on top of the filter. Stand away from the open spout and turn it to the left while the pump is on.

This process will flush all of the excess air out of the system, filling the lines with water from the pool. Remember, you have to manually prime the pump with the steps above.

Other reasons your pump won’t prime completely include:

  • There’s too much pressure on the filter gauge. Turn off the pump and clean the filter cartridges to lower the PSI to the manufacturer’s recommended guidelines.
  • The pump’s impeller is jammed. The impeller is located in front of the motor. Its sole purpose is to pull water from the pool and push it through the filter. If it’s jammed, the pump can’t move quickly enough. You’ll need a new impeller from the company’s part number catalog.

Pool Pump Won’t Prime After Vacuuming? Here’s What To Do

Pool vacuums demand a lot of pressure from the pump. If you move the vacuum too quickly, there’s a high chance it’ll pull air into the lines.

So, what can you do to fix a pump that won’t prime after vacuuming?

  1. Turn off the pump and disconnect each of the vacuum hoses.
  2. Keep the vacuum underwater and fill each vacuum hose with water.
  3. Connect the hoses to the vacuum without letting them above the surface.
  4. Keep the final hose union underwater and connect it to the inlet or outlet that it connects to.
  5. Turn on the pump and open the air relief valve on the filter to remove excess air from the system.

Your pool vacuum might require too much PSI from the pump. We suggest getting the previously mentioned booster pump (the Polaris PB4-60) to provide an additional booster.

This pump will work with your main pump to stop it from losing its prime every time you run the pool vacuum.

Pool Pump Won’t Prime After Backwash? Here’s What To Do

Sand filters and DE filters need to be backwashed every few months. This process removes the built-up debris, lowering the filter’s pressure. However, you might have an issue priming the pump if something goes awry.

All pumps need to be primed after the filters are cleaned. Follow the steps mentioned above to prime your pool pump.

Remember to fill the pump basket with hose water until it overflows, then seal the lid. Open the air relief valve on top of the filter to let out all of the excess air.

Another issue could be the filter’s seal. All filters have a body or lid gasket. These massive gaskets can move around and get misaligned when they’re being cleaned.

Turn off the pump and align the gasket and lid to prevent air from getting into the system.

Note: Don’t forget to turn the multiport valve on all sand filters and DE filters back to the filtering setting. Never keep the multiport valve on the backwash setting when you’re running it through the swimming pool, or the pump won’t prime.

Pool Pump Won’t Prime After Freeze? Here’s What To Do

Freezing temperatures can cause severe damage to swimming pools. Not only can it crack the gunite, but it can also damage the plumbing, unions, O-rings, and equipment. Water expands when it freezes, which can warp the parts.

If your pool pump doesn’t prime after a freezing night or day, you might have to hire a professional. They can look for small cracks.

You can prevent this issue from happening by keeping the pump running at a low speed when it’s supposed to be freezing outside. The slight water movement stops it from freezing.

Wait for the ice to thaw before running the pump. Frozen chunks of ice can rip through filter cartridges and pump baskets.

Pool Pump Won’t Prime From Main Drain? Here’s What To Do

If your pump won’t prime from the main drain, it means there’s a crack in the plumbing between the drain and the pump. Pool pumps are rarely primed from the main drain these days.

The drains are inefficient and don’t provide good circulation. You can also replace the main drain lid with a like-for-like model if you think it’s chipped or clogged.

Another suggestion is to turn the valve in front of your pump away from the main drain. It’s always better to pull water from the skimmer than the drain. Look for a multiport valve in front of the pump and check for labels before turning the lever.

Pool Pump Won’t Prime When Vacuuming? Here’s What To Do

If your pump won’t prime when you’re vacuuming, but it’s fine during normal use, you need a booster pump. Pool vacuums use a lot of your pump’s pressure.

Some pumps aren’t designed to handle a vacuum’s demanding strain. The aforementioned Polaris PB4-60 Booster Pump is the top choice for reliability, functionality, and affordability.

Look for floating hoses. These hoses should be underwater if there’s no air in them. A floating hose is a clear indication of air in the lines. Open each hose, push it underwater, and let water into it.

Pool Pump Troubleshooting Resources

If you have any other issues with your pool pump, check out our other pool pump troubleshooting articles: