What priming means and why your jet pump needs it
Priming means filling the pump chamber and intake line with water so the pump can create the suction needed to draw water up from your well. A jet pump cannot pull air—it needs water already present to work. When your pump loses its prime (usually after you drain the system, replace a component, or lose power during a dry spell), it will run but produce no water until you refill that chamber.
You will know your pump has lost its prime if it runs but delivers no water, or if you hear it cycling on and off rapidly without building pressure. The pump is trying to create suction in an empty chamber, which it cannot do.
Key Takeaways
- Priming fills the pump chamber with water so it can create suction to draw water from the well.
- You will need a bucket of water, a wrench to fit your pump's priming plug, and access to the pump's highest point.
- The priming plug is usually a small bolt on top of the pump body or on the discharge line near the pump.
- After pouring water in and replacing the plug, run the pump for a few minutes to confirm it draws water from the well and builds pressure.
- If the pump will not hold prime after repeated attempts, the problem is usually a leak in the intake line or a failed check valve, which requires professional repair.
Locate the priming plug on your pump
The priming plug is a small bolt, usually 1/4 inch to 1/2 inch, located at the highest point of the pump body or on the discharge line (the pipe carrying water out of the pump). On most jet pumps, it sits on top of the pump casing itself. On some models, it is on a small vertical pipe attached to the pump.
If you cannot find it by looking, check your pump's nameplate or manual for the model number, then search online for a diagram. The manual will show you exactly where it is. If you no longer have the manual, the model number is usually stamped on a metal plate bolted to the pump housing.
Do not confuse the priming plug with the drain plug (which is at the bottom of the pump) or the pressure relief valve (which is usually larger and on the side of the tank).
Gather water and tools before you start
You will need a bucket of water—at least 2 to 3 gallons—and a wrench or socket that fits the priming plug. Have the bucket and wrench ready before you open the pump, so water does not spill while you are searching for tools.
If the priming plug is stuck or corroded, spray it with penetrating oil (like WD-40) and wait 10 to 15 minutes before trying to loosen it. This prevents you from stripping the bolt or damaging the pump casing.
Remove the plug and pour water into the pump
Using your wrench, turn the priming plug counterclockwise to loosen it. Once it is loose enough, unscrew it by hand and set it aside where you will not lose it. Water may drip out—this is normal.
Slowly pour water from your bucket into the opening until water begins to overflow slightly from the hole. This means the pump chamber is full. Stop pouring once you see water coming out; do not overfill. Replace the priming plug by hand first, then tighten it with your wrench. Do not over-tighten, or you may crack the pump casing or strip the threads.
Run the pump and listen for water flow
Turn on the pump at the switch or breaker. The pump should start when ready. Listen for the sound of water moving through the discharge line. Within 30 seconds to 2 minutes, you should hear water flowing and feel pressure building in the tank (if you have a pressure tank, the gauge will begin to rise).
Let the pump run for 2 to 3 minutes to confirm it is drawing water steadily from the well and that pressure is stable. If you have a pressure gauge on the tank, it should climb to your system's normal operating pressure (usually 40 to 60 pounds per square inch, depending on your tank settings).
What to do if the pump will not prime
If the pump runs but no water comes out after 3 to 5 minutes, or if it primes once but loses prime again within hours, the problem is usually a leak in the intake line (the pipe running from the well to the pump) or a failed check valve inside the pump. Both of these require professional repair.
A leak in the intake line allows air to enter, which breaks the seal the pump needs to draw water. A failed check valve prevents water from staying in the pump chamber between cycles. Neither is a repair you can do yourself—call a well pump technician to inspect the intake line for cracks or loose fittings and to test or replace the check valve.
Do not repeatedly prime the pump if it will not hold prime. Each attempt wastes water and can damage the pump if it runs dry for too long.
Prevent future priming problems
Once your pump is primed and running normally, you can reduce the chance of losing prime by keeping the intake line in good condition. Check the visible portions of the intake line (usually in the basement or pump house) for cracks, loose fittings, or corrosion. Tighten any loose connections with a wrench.
If you drain your system intentionally—to replace a filter, repair a fitting, or winterize the house—you will need to prime the pump again afterward. This is normal and expected. Keep your priming plug accessible and your wrench nearby so you can do this quickly.
Frequently Asked Questions
How much water do I need to prime the pump?
Usually 2 to 3 gallons is enough to fill the pump chamber and intake line. Pour slowly until water overflows from the priming hole, then stop. If you pour too much, it straightforward spills out; if you pour too little, the pump will not prime.
Can I prime the pump from the faucet instead of carrying a bucket?
Yes, if you have a faucet close enough to the pump. Use a hose or pitcher to pour water directly into the priming hole. The result is the same—the pump chamber fills with water so the pump can create suction.
Why does my pump lose prime every few days?
A pump that loses prime repeatedly has a leak in the intake line or a failed check valve. Both allow air to enter the system or water to drain back into the well. This requires a professional inspection and repair—do not keep re-priming, as it can damage the pump.
Is it safe to prime the pump myself, or should I call a technician?
Priming is safe to do yourself—it is straightforward pouring water into a hole and tightening a bolt. If the pump will not prime after one or two attempts, or if it loses prime repeatedly, that is when you need a technician to find the underlying problem.
What if the priming plug is stuck and I cannot loosen it?
Spray it with penetrating oil and wait 15 minutes, then try again with a wrench that fits snugly. If it still will not budge, stop—forcing it can break the pump. Call a technician to remove it without damage.