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 shallow well pump cannot move water if air is in the line — it will just spin without pulling anything up. Once you prime it, water fills the space where air was, and the pump can create the suction needed to draw water from the well.
You need to prime a shallow well pump when you first install it, after you drain the system for maintenance, or if the pump has sat unused for weeks. If your pump runs but produces no water, loss of prime is usually the cause.
Key Takeaways
- Priming fills the pump casing and intake line with water so the pump can create suction and pull water from the well.
- You prime through the priming plug or priming port on top of the pump casing — this is where you pour water in before starting the pump.
- The process takes 5 to 15 minutes and requires a bucket of water and a wrench to open and close the priming port.
- If water leaks from the priming port after you close it, the seal may be worn and the pump may lose prime again after a few days of running.
Locate the Priming Port on Your Pump
The priming port is a small plug or valve on the top or side of the pump casing. On most shallow well pumps, it sits directly above the impeller chamber. Look for a bolt or screw-in plug roughly the size of a quarter or half-dollar — it may be labeled "prime" or have a small air vent symbol.
If you cannot find it, check your pump manual for the exact location. Different manufacturers place it in slightly different spots. Some pumps have a priming port and a separate air vent; if yours has both, you will open the air vent after priming to let trapped air escape.
Prepare the Pump and Gather Water
Turn off the pump before you begin. If the pump is electric, switch off the breaker. If it is gas-powered, turn the fuel valve to off. Do not start the pump while you are priming — you are filling it by hand first.
Gather a bucket of clean water from a hose, a faucet, or stored water. You will need roughly 2 to 5 gallons depending on the pump size — a standard shallow well pump casing holds about 1 to 2 gallons, but you may need extra to fill the intake line as well. Have a wrench or adjustable wrench ready to open and close the priming port.
Open the Priming Port and Pour Water In
Use the wrench to slowly unscrew the priming port plug. Turn it counterclockwise until it comes free. Water or air may escape — this is normal. Set the plug aside where you will not lose it.
Position your bucket under the port to catch any spillage. Slowly pour water into the opening until water begins to overflow from the port. This means the casing and the line above it are full. Stop pouring once water flows out steadily — you do not need to overfill.
Close the Port and Start the Pump
Screw the priming port plug back in by hand first, then tighten it with the wrench. Turn it clockwise until it is snug — do not over-tighten, as this can crack the fitting or strip the threads. The plug should be tight enough that water does not drip from it.
If your pump has a separate air vent valve, open it now by turning the screw counterclockwise one or two turns. This lets air escape as the pump starts. Turn on the pump (switch the breaker or fuel valve back on). The pump should begin to pull water from the well within 30 seconds to 2 minutes. You will hear the sound change as water enters the line.
Watch for Water Flow and Close the Air Vent
Listen and watch the pump for the first minute or two. You should hear water flowing and feel vibration as the pump works. If you have an air vent open, water or a small amount of air may spray from it — this is the trapped air leaving the line.
Once water flows steadily from the air vent (or after 1 to 2 minutes if there is no vent), close the vent by turning the screw clockwise. The pump is now primed and should continue to run normally. Check the priming port for leaks — a small drip is normal for the first few minutes, but steady water flow means the seal is worn and the pump may lose prime again soon.
Troubleshooting If the Pump Does Not Prime
If the pump runs but no water comes out after 2 to 3 minutes, the intake line may have a leak or the well may be too deep for a shallow well pump. Shallow well pumps work only down to about 25 feet; if your well is deeper, you need a jet pump or submersible pump instead.
Check the intake line for cracks or loose fittings. If the line is cracked, water leaks out instead of being pulled up, and the pump cannot prime. Tighten all fittings at the pump and at the well head. If the line is visibly damaged, it will need to be replaced before the pump can work.
If priming fails repeatedly, the pump impeller or seals may be worn. Worn seals cannot hold the water in the casing, and the pump loses prime within hours of running. A pump that cannot hold prime for more than a day or two will need internal repair or replacement.
Frequently Asked Questions
Can I use any water to prime the pump?
Yes. Use water from a hose, faucet, or bucket. If your well water is very sandy or silty, use clean water from another source if possible — sand in the priming water can scratch the impeller seals. Once the pump is running, it will draw from your well normally.
What if water leaks from the priming port after I close it?
A small drip for the first few minutes is normal as the seal settles. If water streams out, the seal is worn. Tighten the plug slightly with the wrench, but do not force it. If leaking continues, the seal will need to be replaced, and the pump may lose prime again after a few days of running.
How often do I need to prime the pump?
Once primed, a healthy pump should hold prime indefinitely. If you have to prime it every few days or weeks, the intake line has a leak or the pump seals are worn. Check the intake line for cracks and have the pump inspected by a well technician.
Can I prime the pump while it is running?
No. Always turn off the pump before opening the priming port. Pouring water into a running pump can damage the impeller or cause water to spray unexpectedly. Prime only when the pump is off.
What if the well is dry or the water level is very low?
A shallow well pump cannot pull water from deeper than about 25 feet. If the well is dry or the water table has dropped below that depth, the pump will not work no matter how many times you prime it. You may need to wait for the water table to rise, drill a deeper well, or switch to a submersible pump designed for deeper wells.