What priming means and why deep well pumps need it
Priming is filling the pump casing and intake line with water before you start the pump. A deep well pump sits below the water table — sometimes 25 feet down or more — and it cannot pull water up through an empty pipe on its own. Air takes up space that water should occupy, and the pump will just spin air until it cavitates (makes a grinding noise) and loses pressure. Priming removes that air pocket so water can flow the moment you turn the pump on.
You will know your pump needs priming if you turn it on and hear it running but get no water at the tap, or only a trickle. This happens after you have drained the system for repairs, replaced a pressure tank, or if the pump has sat unused for weeks. The good news is that priming is a straightforward task you can do yourself in about 15 minutes.
Key Takeaways
- Priming fills the pump casing and intake line with water so the pump can push water up from the well instead of just spinning air.
- You will need a bucket of water, a funnel (or a cup), and access to the priming plug or priming port on top of the pump head.
- Pour water into the priming port until it overflows, then close the plug, turn on the pump, and wait for steady pressure at the tap.
- If water does not appear within 30 seconds of running the pump, stop it and repeat the priming step — do not run a dry pump for more than a minute.
- A pump that will not hold prime after repeated attempts may have a leak in the intake line or a failed check valve, and you should call a well service technician.
Locate the priming plug on your pump
The priming plug (also called a priming port or air vent) is a small bolt or cap on the top of the pump head — the metal housing that sits above ground. On most submersible deep well pumps, it is a 1/4-inch or 3/8-inch bolt with a square head or a slotted top. On some older or larger systems, it may be a threaded port with a removable cap.
If you cannot find it, check your pump's manual or look for a small bolt that is separate from the main discharge line (the pipe that carries water to your house). The priming plug should be at the highest point of the pump casing. If your pump is a jet pump (a different type that sits above ground), the priming port is usually on the side of the pump body and is easier to spot.
Gather water and tools
You will need a bucket of water — at least 2 to 3 gallons — and a way to pour it into the priming port. A funnel works best, but a cup or small pitcher will do. Have a wrench or socket that fits the priming plug bolt so you can remove and replace it. Keep a rag nearby to catch any water that spills.
Use water from a hose, a faucet, or even a neighbor's well if your own system is not producing water. The water does not need to be filtered or special — it is just there to fill the line. If you are priming after a repair, make sure the system is off and depressurized before you start.
Remove the priming plug and pour water in
Use your wrench to loosen and remove the priming plug. Water or air may come out — that is normal. Position your funnel over the opening and pour water slowly into the priming port. Keep pouring until water overflows from the hole and runs down the side of the pump. This tells you the pump casing and the intake line are now full of water, not air.
Do not rush this step. Pouring slowly gives air bubbles time to escape and ensures the entire line fills. If the water level drops as you pour, keep adding more until it stays full and overflows. Once it overflows steadily, you are ready to close the plug.
Close the plug and start the pump
Screw the priming plug back in by hand first, then tighten it with your wrench. Do not over-tighten — snug is enough. Turn on the pump using your pressure switch or control panel. You should hear the pump motor start and feel it vibrate slightly.
Watch the pressure gauge on your pressure tank (if you have one) or listen for water to flow at a nearby faucet. Within 10 to 30 seconds, you should hear water moving through the pipes and see pressure building. If you have a faucet open, water should start flowing within that time. If nothing happens after 30 seconds, turn the pump off when ready — running a dry pump damages the seals inside.
What to do if the pump does not produce water
If you have primed the pump once and it still will not deliver water, turn it off and wait a few minutes. Then repeat the priming step: remove the plug, pour water in until it overflows, close the plug, and start the pump again. Sometimes a second priming is needed if air pockets remain in the line.
If the pump still produces no water after two or three priming attempts, or if it loses prime within a few hours of running, there is likely a leak in the intake line or a failed check valve (a one-way valve that keeps water from flowing backward). These problems require a well service technician to diagnose and repair. Do not keep running the pump dry — it will overheat and fail.
How to prevent future priming problems
Once your pump is primed and running, it should stay primed as long as the system is sealed and the intake line has no leaks. Check your pressure tank's air charge once a year — a tank with the wrong air pressure can cause the pump to cycle on and off too often, which stresses the seals.
If you drain the system for repairs or winterization, write down the steps you took to prime it so you can repeat them exactly when you refill. Keep your pump manual in a safe place and note the location of the priming plug so you do not have to hunt for it in an emergency. If you live in a cold climate, insulate the pump head to prevent freezing, which can crack the casing and introduce air leaks.
Frequently Asked Questions
Can I prime the pump without turning it on?
Yes — in fact, you should prime it before you turn it on. Filling the casing with water and letting it sit for a few minutes can help air bubbles rise and escape. But you still need to start the pump to draw water up from the well. If the pump runs for more than a minute without producing water, turn it off to avoid damage.
What if I cannot find the priming plug?
Check your pump manual first — it will show the exact location and size. If you do not have the manual, contact the pump manufacturer with your model number, or call a local well service company. They can locate it for you and show you how to prime in the future. Do not guess and drill a hole — you could damage the pump.
Is it normal for the pump to make noise after priming?
A little noise is normal as air bubbles work their way out of the line. You may hear gurgling or a brief grinding sound. But if the noise continues for more than a minute or sounds like metal grinding, turn the pump off. This usually means the pump is still running dry and needs another priming attempt.
How often do I need to prime my pump?
A healthy pump should not need priming more than once every few years, and only after you have drained the system. If you find yourself priming every few weeks or months, the system has a leak or a failed check valve. Have a well technician inspect the intake line and pressure tank to find the source.
Can I use a garden hose to prime instead of a bucket?
Yes, if you have access to running water from another source. Attach the hose to the priming port with an adapter (you may need to ask a hardware store for the right size), or straightforward hold the hose over the opening and pour water in. A bucket is simpler because you do not need adapters and you can control the flow better.