When your swimming pool pump starts and the water doesn’t circulate around the system your pump is not primed for normal operation. The pump basket may remain empty or repeatedly fill and empty with water indicating the pump is struggling to draw enough water from the pool.
Learn how to prime a swimming pool pump by filling the filtration system with water and removing all the air pockets in the system. A pool filtration system is a water tight system and does not work well with air in the system. The most common reason for a pump basket not filling with water and reaching prime is the pool water level is too low. Other common reasons are the skimmer weir flap is stuck, the pump impeller is clogged, or there is an incorrectly positioned valve or an air leak in the system.
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Pool Pump Basket Does Not Fill with Water
A pool filtration system is a water tight system. The pump draws water from the pool , passes it through the filter for cleaning and pushes the water back into the pool. The pump drives two important activities – filtering and circulating the pool water.
Normally, a filtration system works very well until you get air in the system.
When a swimming pool pump starts there may be air remaining in the system which prevents the pump from drawing water from the skimmer box into the pump basket. The pump basket may repeatedly fill and empty with water indicating the pump is struggling to draw enough water from the pool. Or maybe the pump basket does not fill with any water.
Air is pumped into the filter tank where it is trapped and compressed at the top of the tank. Now the filter cannot operate effectively and water is not circulating around the pool.
Read on to discover how to prime a swimming pool pump quickly and easily.
What is Priming a Pool Pump?
Priming the pool pump means eliminating the trapped air pockets and filling the filtration system with water to start it up.
The pump must be full of water to operate effectively and to drive water through the filtration system. When the filter operates at the right pressure it effectively cleans and circulates the pool water. Otherwise the pump keeps straining to draw water from the pool and cannot circulate water through the system.
When Do You Need to Prime a Pool Pump?
You need to prime a pool pump when there are air pockets in the filtration system and the pump basket does not fill with water.
Air becomes trapped in the filtration system for the following reasons:
- The pump basket was opened for cleaning and water drained away back into the skimmer box and pool. The pump basket was closed leaving an air pocket in the pump.
- Opening and cleaning the filter cartridge will leave an air pocket in the filter tank.
- The pool water level is too low causing the skimmer box to become partially empty when the pump draws water into the filter plumbing. The pump sucks in air and causes an air pocket in the filter tank.
- When the skimmer box weir flap becomes stuck with debris it can cause the box to run dry when the pump is running. The pump sucks in air and causes an air pocket in the filter tank.
- The pool was prepared for the winter by flushing water from the filtration system and plumbing to prevent water freezing in the pipes. Now you are opening the pool for the summer season and need to remove air in the system.
- The pool was emptied and water drained from the plumbing pipes. When the pool was refilled with water it created air pockets in the filtration system.
- An incorrectly positioned pump valve or multiport valve may allow air to be drawn into the plumbing from the drain.
- A pump valve or multiport valve with a worn gasket seal may allow air into the system.
- There may be a leak in the pipe connections or pump basket lid allowing air into the system.
How to Prime a Swimming Pool Pump
Check the Filtration System for Leaks
- Ensure the filter tank drain plugs are not leaking when the pump is operating. If they are leaking remove the plugs and wrap plumber’s Teflon tape clockwise around the threads and replace the plugs. If there is an O-ring seal on the plug replace it with a new O-ring seal.
- Remove the filter tank lid (cartridge filter system) and check the O-ring seal. Replace the seal if it is worn or damaged. Replace the lid and make sure the seal is watertight. You can add silicone lubricant to the lid screw fitting to help get a good seal and make it easy to open again in the future.
- Check the pressure gauge by unwinding the gauge from the filter lid and checking the seal and thread. If necessary, wrap plumber’s Teflon tape clockwise around the thread and replace the pressure gauge.
Refer to our article on Pool Filter Pressure Gauges for more information
Check the Skimmer Box & Water Level
- Check the skimmer weir flap is moving freely and the skimmer box is full of water.
- Ensure the pool water level is at the midway mark of the skimmer weir flap. If the water level is too low add water to the pool with the garden hose. If the water level is high that’s ok for our test because we are going to pump water into the drain and the water level will drop slightly.
Refer to our article on How a Pool Skimmer Box Works for more information
Prime the Swimming Pool Pump
- Set the multiport or pump valve to the waste position so water will be drawn from the pool and pumped into the drain. This provides the path of least resistance for the pool pump to operate as there is no filter in the way. All we are trying to do at this stage is prime the system and remove any air pockets.
- If you have a sand filter you can set the multiport valve to the recirculate position to bypass the filter. This will also provide a path of little resistance.
- Turn off the power supply to the pump.
- Open the pump basket and remove the basket. Put a screw driver into the pump and wiggle it around to remove debris from the impeller inside the pump.
- Replace the pump basket and fill the pump with water. Use the garden hose and make sure you get any air pockets out of the pump. As you fill the pump the water may run back into the pipes so just keep filling until the pump is full of water.
- Replace the pump lid ensuring there is a water tight seal. Replace the pump basket lid seal if it is worn or leaking.
Run the Pump to Waste
- Turn on the power to the pump.
- If you have a dual speed or variable speed pump ensure the pump is set to high power to prime the pump.
- The pump basket should remain filled with water and the system reach prime within one minute. The pump basket may empty and refill with water many times before it eventually remains full of water with no air pockets.
- The water is passing through the pump and into the drain.
- Turn off the pump.
Run the Pump to the Filtration System
- Set the valve to filter.
- You can also fill the cartridge filter tank with water to remove all the air in the tank.
- Open the air bleeder on the top of the filter tank to allow air to escape the system.
- Turn on the pump
- When water shoots out of the air bleeder on the top of the filter tank close it. You have now removed the air pocket from the filter tank.
- Once the pump basket is full of water the pump is primed and the filtration system will operate normally.
How to Prime a Swimming Pool Pump with Multiple Skimmer Boxes
If you have a large swimming pool with more than one skimmer box you should work on getting one skimmer box line working at a time.
Set your valves to close off all but one skimmer box. Perform the above procedure to prime the pump and eliminate air pockets from the system.
Once you have the pump primed and running well and no air in the system open up another skimmer box with the valve for that line. Try to partially open the valve first so that you do not overwhelm the pump by the extra work of sucking air into system. It’s a process of gradually opening the valve to bring the next skimmer box online and remove the air out of the line. You will need to open the pressure relief valve on the top of the filter tank again until water shoots out.
Note: Don’t try to turn the valve when the pump is running. Always switch off the pump before turning the valve.
Frequently Asked Questions
What Happens When a Pool Pump Runs Dry?
Most pool pumps are water cooled so if the pump runs dry it will begin to overheat especially if operating in summer conditions. The high heat and stress on the pump will damage the motor and seals.
Why Does My Pool Pump Lose Pressure When Vacuuming?
The reduction in pressure could be caused by a number of issues.
- The vacuum hose may have a blockage or partial restriction causing the water flow to drop and strain the pump motor.
- The hose may have a split or leak which is drawing in air to the pump.
- The vacuum plate in the skimmer box may not be producing a good seal.
- The plate should be completely underwater to reduce the chance of introducing air to the system.
- The pump basket may be clogged with debris.
- The pump basket lid may have a leak allowing air in to the pump.
- The filter may have become clogged with debris. Clean the filter. If the pool is very dirty try vacuuming to waste to clean the pool and not clog the filter.
Or you may have introduced an air pocket when connecting the vacuum hose to the skimmer box plate or pipe. Before connecting up the vacuum hose hold it over an outlet jet with the pump running to expel air from the hose.
Try vacuuming to waste to see if that causes a drop in pressure. If there is no drop in pressure then your filter needs cleaning or replacement of the cartridge.
Why is my pool pump not pumping water?
Apart from having an air pocket in the system it can be caused by an obstruction in the plumbing or pump. Check the skimmer basket and pump basket is clean. Clear any debris from the pump impeller. Check for air leaks in the system.
