What Priming Means and Why Your Pump Needs It
Priming means filling the pump casing and intake line with water before you start the pump. A well pump cannot move air—it moves only water. If air gets trapped inside, the pump will spin uselessly and overheat, and you will get no water at the tap. Priming pushes that air out and fills the space with water so the pump can do its job.
You need to prime a pump after you first install it, after you drain the system for repairs, or after the water level in your well drops so low that the intake line sucks in air instead of water. If you turn on the pump and hear it running but no water comes out, the pump has lost its prime and needs priming again.
Key Takeaways
- Priming fills the pump casing and intake line with water so the pump can push water instead of air.
- You prime by pouring water into the priming port (a plug or opening on top of the pump) until water comes out the discharge line or until the pump starts moving water on its own.
- The priming port is usually a threaded plug on the pump housing itself—check your pump's manual to find its exact location.
- If your pump has a check valve on the intake line, you may need to open a bleeder valve on the discharge side to let air escape while you prime.
- Priming usually takes 5 to 15 minutes; if water does not flow after 20 minutes of pouring, the intake line may be cracked or the well may be dry.
Locate the Priming Port on Your Pump
The priming port is a small opening on the pump housing, usually on the top or side. It is often a threaded plug that you can unscrew by hand or with a wrench. On some pumps it is a small valve. Check your pump's manual or the manufacturer's label on the pump itself to find the exact location—different pump models put it in different spots.
If you cannot find a priming port, your pump may be a submersible model (installed inside the well) or a sealed type that primes itself. Submersible pumps do not need manual priming. If you have a centrifugal pump above ground and cannot locate a port, contact the pump manufacturer with your model number.
Gather Water and Tools
You will need a bucket or pitcher of clean water—at least 2 to 3 gallons to start. Use water from a hose, faucet, or rain barrel; do not use well water if the well is the problem. You will also need an adjustable wrench or socket wrench that fits the priming port plug, and a rag or old towel to catch spills.
If your pump has a check valve on the intake line (a one-way valve that prevents backflow), you may also need to open a small bleeder valve on the discharge line—the pipe carrying water away from the pump. This lets trapped air escape while you pour water in. Your manual will tell you if your system has a bleeder valve and where it is.
Remove the Priming Port Plug and Pour Water
Turn off the pump at the switch or breaker before you start. Use your wrench to unscrew the priming port plug slowly—water or air may spray out, so point it away from your face. Once the plug is out, set it somewhere you will not lose it.
Place your bucket under the opening to catch overflow. Pour water slowly into the priming port, filling it until water comes out the discharge line (the outlet pipe) or until the casing is completely full. This usually takes 2 to 5 gallons. If your system has a bleeder valve on the discharge side, open it first so air can escape; close it once water starts flowing out.
Start the Pump and Watch for Water Flow
Once the casing is full, screw the priming port plug back in firmly—do not overtighten it, or you may strip the threads. Turn the pump on. Listen and watch the discharge line. Within 30 seconds to 2 minutes, water should start flowing. If it does, the prime is successful and you can close any bleeder valves you opened.
If no water flows after 2 to 3 minutes, turn the pump off and wait 5 minutes. Then repeat the priming process: unscrew the plug, pour in another 2 to 3 gallons of water, screw the plug back in, and start the pump again. Most pumps prime on the second or third attempt. If water still does not flow after three tries, the intake line may be cracked, the well may be dry, or the pump itself may be damaged.
Common Mistakes That Prevent Priming
The most common error is not filling the casing completely before starting the pump. If even a pocket of air remains, the pump will not move water. Pour slowly and fill until water reaches the top of the opening or comes out the overflow.
Another mistake is forgetting to close a bleeder valve after priming. If you leave it open while the pump runs, air will enter the system and you will lose the prime again. Close any bleeder valves as soon as water flows out of them. Also, do not use the pump's discharge tap to fill the casing—use the priming port only. Filling from the tap will not push air out of the pump housing.
When to Call a Professional
If the pump runs but produces no water after three priming attempts, or if water flows for a few seconds and then stops, the problem is likely not the prime. The intake line may have a leak, the well may have run dry, or the pump may be damaged. These issues require a well technician to diagnose.
If you hear a grinding or squealing noise from the pump while it runs, turn it off when ready—running a pump without water damages the seals and bearings. Do not attempt to prime again; call a technician instead. Also, if the priming port plug is stuck or stripped, do not force it; a professional can remove it without damaging the pump.
Frequently Asked Questions
How do I know if my pump has lost its prime?
The pump will run but no water will come out of any tap in the house. You may also hear the pump humming or see it cycling on and off without building pressure. If the pressure gauge on the tank drops to zero, the prime is lost.
Can I use well water to prime the pump?
No. If the well is contaminated or the intake line is drawing in sediment, using well water to prime will make the problem worse. Use clean water from a hose, faucet, or stored rainwater instead.
What if water leaks out around the priming port plug when I screw it back in?
The threads may be dirty or slightly damaged. Unscrew the plug, wipe both the plug and the opening with a clean rag, and screw it back in firmly but not forcefully. If it still leaks, the seal may be worn and the plug may need replacement.
How long should priming take?
Most pumps prime within 5 to 15 minutes of pouring water and starting the pump. If water does not flow after 20 minutes, stop and wait 5 minutes before trying again. Repeated attempts over more than an hour suggest a deeper problem with the intake line or well.
Do I need to prime my pump every time I use it?
No. Once primed, the pump should hold its prime as long as the system stays sealed and the well has water. You only need to prime again if the pump loses water pressure, if you drain the system for repairs, or if the well level drops below the intake line.