What priming means and why your pump needs it
Priming means filling the pump and the intake line with water before you start it. A submersible well pump sits at the bottom of the well and pushes water up through a long pipe to your house. If that pipe is full of air instead of water, the pump will run dry — it cannot create the pressure needed to pull water up from below, and it will burn out in minutes.
Priming fills the pipe so the pump has something to work with from the moment it starts. Without it, you risk damaging the pump impeller and seals, which are expensive to replace. If your pump has been off for more than a few hours, or if you have just installed it, priming is not optional.
Key Takeaways
- Priming means filling the discharge pipe with water before starting the pump so it does not run dry and damage itself.
- You prime by pouring water into the top of the discharge pipe or into a priming port on the pump head until water flows back out, then closing the valve and starting the pump.
- If your well is shallow (under 25 feet), you can usually prime from the top; deeper wells may need a priming port or a check valve installed by a professional.
- A pump that loses prime repeatedly may have a leak in the discharge line, a faulty check valve, or an air leak at a connection — each requires a different fix.
Locate the priming port or discharge pipe opening
Before you start, turn off the pump at the breaker. You need to find where water goes into the system. On most submersible pumps, this is either a priming port (a small threaded opening on top of the pump head) or the main discharge pipe (the large pipe that runs from the pump to your house).
If your pump was installed by a professional, there may be a priming port with a cap or valve already in place. If you see a T-shaped fitting or a ball valve on the discharge line near the pump head, that is likely your priming port. If there is no port and you cannot safely access the top of the discharge pipe, you will need a plumber to install one — do not attempt to cut into a pressurized line.
Check your pump manual or the paperwork from installation. The manual will show exactly where to pour water and whether your model has a priming port or requires a different method.
Gather water and a container
You will need clean water — well water, tap water, or rainwater all work. Bring a bucket, a hose, or a jug with enough water to fill the discharge pipe. For a typical residential setup, this is usually 5 to 15 gallons, depending on how deep your well is and how long the pipe is.
If your well is very deep (over 100 feet), you may need more water than you can reasonably pour by hand. In that case, a plumber can use a priming pump or a pressure tank to do the job faster and more reliably.
Pour water into the priming port or discharge opening
Remove the cap from the priming port or the top of the discharge pipe. Slowly pour water in while watching for it to flow back out or to stop accepting water. Keep pouring until water comes out the top — this means the pipe is full and air has been pushed out.
If you are priming through the discharge pipe itself (not a dedicated port), you may see water back up and overflow. This is normal. Stop pouring once water is flowing steadily out the top or once the pipe will not accept any more.
Do not rush this step. Pouring too fast can trap air pockets in bends or high spots in the line. Pour slowly and steadily, and wait a few seconds between pours to let air escape.
Close the valve and start the pump
Once the pipe is full, cap or close the priming port when ready. If you left it open and started the pump, water would spray out and you would lose prime. Screw the cap back on hand-tight — you do not need to force it.
Turn the pump on at the breaker. You should hear it start and feel vibration. Within a few seconds, water should come out of your faucets or into your pressure tank. If nothing happens after 30 seconds, turn the pump off and repeat the priming process — you may have trapped an air pocket.
What to do if the pump loses prime repeatedly
If you have to prime the pump more than once a month, something is wrong. The most common cause is a leak in the discharge line — even a small hole will let air in and water out. Check the entire pipe from the pump head to where it enters your house. Look for wet spots, drips, or mineral stains.
The second most common cause is a faulty check valve. This one-way valve sits on the discharge line and stops water from flowing backward into the well when the pump is off. If it leaks, water drains out of the pipe overnight, and you have to prime again in the morning. A plumber can test the check valve by closing the isolation valve and watching whether pressure holds.
A third possibility is an air leak at a connection — a loose fitting, a cracked union, or a bad seal where the discharge line connects to the pump head. Tighten all visible fittings by hand first. If that does not stop the leak, the connection may need to be taken apart, cleaned, and reassembled with fresh thread seal tape or plumber's putty.
When to call a plumber
If your well is deeper than 25 feet and has no priming port, installing one requires cutting into the discharge line and soldering or threading a new fitting. This is not a safe DIY job — a mistake can crack the line or create a leak that ruins your pump.
If priming does not restore water pressure, or if the pump runs but no water comes out, the problem is likely below ground — a broken intake line, a clogged screen, or a failed pump. These require pulling the pump out of the well, which needs a licensed well contractor with the right equipment.
If you see water pooling around the well cap or hear hissing from the pump head, stop using the pump when ready and call a plumber. These are signs of a serious leak or internal failure.
Frequently Asked Questions
How often should I prime my submersible pump?
A healthy pump should hold prime indefinitely once started. If you have to prime more than once a month, you have a leak or a faulty check valve. A pump that needs priming every time you turn it on has lost its ability to hold a vacuum and may be failing internally.
Can I prime a submersible pump from the top of the well?
Yes, if you can safely reach the discharge pipe or priming port. For shallow wells (under 25 feet), pouring water down the pipe works fine. For deeper wells, gravity makes it harder to fill the entire line, and a priming port closer to the pump head is more effective.
What happens if I start the pump without priming it?
The pump will run dry and overheat within seconds. The impeller spins without water to cool it, and friction damages the seals and bearings. Even 30 seconds of dry running can shorten the pump's life by years. Always prime before starting a pump that has been off for more than a few hours.
Is it normal for water to spray out when I prime?
Yes. As you pour water in, air gets pushed out and water may overflow from the priming port or the top of the discharge pipe. This is how you know the line is filling. Once water flows steadily without air bubbles, cap the port and start the pump.
Can I use a garden hose to prime instead of pouring by hand?
Yes, if you have a hose long enough to reach the priming port and a water source nearby. A hose is faster and easier than carrying buckets, especially for deep wells. Just make sure the water pressure is low enough that you do not force water into the pump faster than air can escape.