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 pull water up from the ground on its own — it needs water already inside the system to create the suction that draws more water up. Without priming, the pump will run dry, overheat, and fail.
Shallow well pumps sit above ground and pull water from depths of 25 feet or less. The deeper the well, the more critical priming becomes. If your pump has been sitting unused, the water inside has drained back down the line, and you must refill it before starting the motor.
You will know your pump needs priming if it runs but produces no water, makes a loud grinding noise, or shuts off after a few seconds. These are signs the pump is cavitating — running without water inside — and will damage itself if you do not stop it.
Key Takeaways
- Priming fills the pump casing and intake line with water so the pump can create suction and pull water from the well.
- Locate the priming plug (usually a large bolt on top of the pump) and remove it to access the fill opening.
- Pour water into the opening until it overflows, then replace the plug and start the pump when ready.
- If the pump loses prime repeatedly, the intake line may have a leak or the check valve may be stuck, and you should inspect both before priming again.
- Priming takes 5 to 15 minutes and should be done before the pump sits unused for more than a few days.
Locate the Priming Plug on Your Pump
The priming plug is a large bolt or cap, usually brass or steel, mounted on the highest point of the pump casing. On most shallow well jet pumps, it sits on top of the motor housing or on the side of the pressure tank. On centrifugal pumps, it is often on the pump head itself.
Check your pump's manual or the manufacturer's label to confirm the location. If you cannot find the manual, look for a metal tag on the pump body that lists the model number — you can search that number online to find a diagram. The priming plug is always at the highest point because air rises and water sinks; you need to fill from the top to push all air out.
Some pumps have a priming valve instead of a plug — a small lever or knob that you turn to open. Either way, the principle is the same: you are opening a path to pour water directly into the pump casing.
Prepare Your Water Source and Container
You will need a bucket or pitcher of clean water and a funnel. The water does not have to be filtered or treated — tap water from a hose works fine. Fill your bucket with at least 2 to 3 gallons; you may need more if the intake line is long or if the pump is very dry.
Place the funnel in the priming opening. If you do not have a funnel, you can use a piece of PVC pipe or even roll up a piece of paper into a cone. The goal is to pour water without spilling it outside the opening and wasting it.
Have your pump switch or breaker within arm's reach. Once you finish priming, you will start the pump when ready, so you do not want to waste time hunting for the switch.
Pour Water Into the Pump Until It Overflows
Pour water slowly into the funnel. Watch the opening — you are filling the pump casing, the intake line, and any pipes connected to the pump. As you pour, air will escape from the system. You may hear gurgling or see bubbles.
Keep pouring until water runs out of the opening and overflows. This means the casing is completely full and all air has been pushed out. Do not stop early — a partially filled pump will not prime.
If the water level drops as you pour, the intake line is longer than you thought, or there is a leak somewhere. Keep pouring until the level stays constant and overflows. This usually takes 1 to 3 minutes.
Replace the Plug and Start the Pump when ready
Once water overflows, quickly remove the funnel and screw the priming plug back in by hand. Tighten it firmly but do not use a wrench yet — hand-tight is enough to seal it. If you over-tighten a brass plug, you can crack it.
Turn on the pump switch or flip the breaker to start the motor. The pump should begin to pull water from the well within a few seconds. You should hear the motor running smoothly and feel water pressure building in the system. If you have a pressure gauge on the tank, watch it rise.
Let the pump run for 30 seconds to 1 minute. Then turn it off and check for leaks around the priming plug. If water is dripping, tighten the plug slightly with a wrench. Once it is sealed, you can turn the pump back on and use it normally.
What to Do If the Pump Loses Prime Repeatedly
If you prime the pump and it works for a day or two, then loses prime again, something is letting air into the system. The most common cause is a leak in the intake line — the pipe that runs from the pump down into the well. Even a tiny hole will let air in and break the seal.
Inspect the intake line for cracks, holes, or loose fittings. If the line is buried, you may not see the leak, but you can feel for wet soil around the well cap. If you find a leak, you will need to replace that section of pipe or tighten the fitting.
The second common cause is a stuck check valve. The check valve sits in the intake line and allows water to flow up but not back down. If it gets stuck open, water drains back into the well when the pump stops, and you lose prime. You may hear a loud clunk when you turn off the pump — that is the check valve slamming shut. If this happens, the valve needs to be replaced.
If you cannot find a leak and the check valve seems fine, the pump itself may have internal damage. In that case, you should have a well technician inspect it.
How Often to Prime and When to Call a Professional
A healthy pump should not need priming more than once every few months, and usually only after it has sat unused for weeks. If you are priming every few days, something is wrong — either a leak, a bad check valve, or a failing pump seal.
If priming does not restore water flow, or if the pump runs but produces only a trickle, the problem may be deeper in the well. The well itself could be running low, the intake screen could be clogged, or the pump could be cavitating internally. These are jobs for a licensed well technician.
Do not run the pump dry for more than a few seconds. Dry running will destroy the pump's internal seals and bearings within minutes. If you hear grinding or squealing and no water comes out, stop the pump when ready and prime it again before running it further.
Frequently Asked Questions
Can I prime the pump with a garden hose instead of pouring from a bucket?
Yes. Attach a hose to a nearby faucet, place the nozzle in the funnel, and turn on the water. This is faster than pouring from a bucket and works just as well. Stop when water overflows, then when ready start the pump.
What if no water comes out after I prime and start the pump?
The pump may not have primed fully, or the well may be dry. Turn off the pump, wait 5 minutes, and prime again. Pour more slowly this time and make sure water overflows for at least 10 seconds. If water still does not flow, the well may have run low or the intake line may be blocked.
Is it normal for the pump to make noise right after priming?
Some noise is normal — you may hear gurgling, hissing, or a brief grinding sound as air escapes and water fills the line. This should stop within 30 seconds. If the noise continues or gets louder, turn off the pump and check that the priming plug is sealed tightly.
How long does priming take?
Pouring water and filling the pump takes 2 to 5 minutes. The pump itself should produce steady water pressure within 30 seconds of starting. If it takes longer than a minute, the intake line may be very long or there may be a partial blockage.
Do I need to prime the pump before every use?
No. Once primed, the pump holds its prime as long as it is used regularly and the system has no leaks. You only need to prime again if the pump has sat unused for several days or if you notice it has lost pressure.