How To Prime A Water Well Pump: A Step-by-Step Guide To Restoring Water Pressure
To prime a water well pump, you must fill the pump casing and the suction pipe completely with water to eliminate trapped air, which prevents the impeller from creating the vacuum needed to draw water. This process requires turning off the electrical power, opening the dedicated priming port, pouring clean water into the system until it overflows, sealing the port securely, and cycling the motor. Properly executing these steps prevents dry-running, cavitation, and catastrophic motor burnout in shallow-well, deep-well, and centrifugal booster pumps.
Essential Safety Protocols, Tools, and Pre-Priming Checklist
Before attempting to prime a water well pump, you must understand the mechanical principles at play. Above-ground pumps, such as shallow-well jet pumps and deep-well jet pumps, are not self-priming. They rely on atmospheric pressure and the physical presence of water within the pump casing (volute) to create a pressure differential. If air enters the system—due to a power outage, a drop in the water table, or a plumbing leak—the pump will spin freely without moving water, a state known as losing prime. Running a pump dry for even a few minutes can melt internal diffusers, destroy rubber gaskets, and burn out mechanical shaft seals.
Preparing your workspace and gathering the correct tools ensures a swift, safe, and successful priming sequence.
- Estimated Duration: 30 to 45 minutes.
- Estimated Budget: $15 to $40 (assuming basic tools are already on hand).
- Mandatory Safety Gear: Safety glasses, heavy-duty work gloves, and a non-contact voltage tester.
- Required Tools and Materials:
- An adjustable pipe wrench or slip-joint pliers (channel locks).
- A clean, five-gallon bucket filled with potable (drinking) water.
- A funnel that fits snugly into the priming port.
- High-quality polytetrafluoroethylene (PTFE) thread sealant tape or non-hardening pipe joint compound.
- A wire brush to clean corroded pipe threads.
How to Prime a Shallow Well or Deep Well Jet Pump: The Step-by-Step Execution
Follow these precise steps to purge air from your well pump system and safely restore your water supply.
Step 1: Isolate and Disconnect the Electrical Power Source
Working with water and high-voltage electricity presents a severe risk of electrocution. Locate the dedicated electrical breaker panel for your well system. Flip the double-pole circuit breaker (typically 230-volt or 115-volt) assigned to the well pump to the "Off" position. If your system uses a fused disconnect switch box near the pump, open the box and pull the disconnect block or flip the switch to off. Use a non-contact voltage tester near the pressure switch terminals to verify that no electrical current is flowing to the unit before touching any metallic components.
Step 2: Relieve Residual System Pressure
An energized pressure tank can back-pressure your pump, making it dangerous or impossible to remove the priming plug. Close the main shut-off valve on the discharge side of the pump (the pipe leading from the pump to your home's water distribution system). Open an outdoor spigot or a faucet located downstream of the pump but upstream of the pressure tank to relieve any remaining hydraulic pressure in the lines. Watch the pressure gauge on the pump manifold; do not proceed until the gauge reads 0 PSI.
Step 3: Locate and Remove the Priming Plug
Identify the priming plug on your pump housing. On most shallow-well and deep-well jet pumps, this is a square-headed or hexagonal bolt located at the highest point on the top of the wet end (the cast iron or plastic volute casing). Do not confuse this with the drain plug, which is located at the very bottom of the casing. Use an adjustable wrench or pipe wrench to turn the plug counterclockwise. If the plug is rusted or seized, apply a small amount of penetrating oil, let it sit for five minutes, and apply steady pressure. Remove the plug completely and inspect its threads for wear or debris.
Step 4: Inspect the System and Prepare the Port
Peer into the open priming port using a flashlight. Look for visible debris, mineral scaling, or rust deposits that could prevent a tight seal or damage the internal impeller. Use a small wire brush to clean the internal female threads of the priming port. Ensure that the nearby pressure switch and electrical connections are draped with a dry towel to protect them from accidental water spills during the next step.
Step 5: Fill the Pump Casing and Suction Line with Water
Insert your funnel into the open priming port. Slowly pour clean, potable water from your five-gallon bucket into the casing. Pouring slowly is critical because it allows air bubbles trapped inside the pump volute and the horizontal suction line to rise and escape through the port.
If you are priming a shallow-well jet pump, you are filling both the pump housing and the entire vertical suction pipe leading down into the well. This may require several gallons of water. If you pour water in and it immediately drains away without filling up, your foot valve (the one-way check valve at the bottom of the well pipe) is likely stuck open or leaking. If the foot valve is operating correctly, the water level will eventually rise to the top of the priming port and remain stable.
Warning: Never use dirty water, pond water, or graywater to prime your pump. Doing so will introduce pathogens and abrasive sediment directly into your home's drinking water system and can ruin the pump's internal seals.
Step 6: Seal the Priming Port
Once the water level stabilizes at the very lip of the priming port, wrap the threads of the priming plug with three to four wraps of PTFE thread sealant tape in a clockwise direction. Alternatively, apply a thin, even layer of non-hardening pipe joint compound to the threads. Thread the plug back into the port by hand to ensure you do not cross-thread the fitting. Use your wrench to tighten the plug securely. Do not overtighten, as cast iron and plastic pump casings can crack under excessive torque.
Step 7: Re-Energize and Cycle the Pump
Open the discharge valve slightly to allow air to escape into the pressure tank or out of a nearby open faucet. Flip the electrical breaker back to the "On" position. The pump motor should immediately start.
Monitor the pressure gauge on the pump. You should see the pressure steadily rise. A successful prime is indicated when the pressure gauge rapidly climbs past 20 PSI and heads toward the cut-out pressure of your system (typically 50 or 60 PSI).
Pro-Tip: If the pump runs for more than two minutes without building pressure, or if you hear a loud, metallic rattling noise (which indicates cavitation due to trapped air), immediately turn off the power. Running the pump dry for longer will cause permanent thermal damage. Let the pump cool completely, remove the priming plug, and repeat Steps 5 through 7. It is common to require two or three priming cycles to completely evacuate air from long suction lines.
How To Prime Goulds Jet Pump | TAFT Independent
Well Pump Operating Specifications and Priming Metrics
Different well depths and pump configurations require varying operational thresholds. Use the table below to verify that your pump is operating within standard industry parameters.
| Pump Type | Maximum Suction Lift Depth | Typical Operating Pressure Range | Priming Water Volume Required | Primary Check Valve Location |
|---|---|---|---|---|
| Shallow-Well Jet Pump | 25 Feet (7.6 Meters) | 30 to 50 PSI | 1 to 3 Gallons | Foot valve at the bottom of the well pipe |
| Deep-Well Jet Pump (Double Pipe) | 110 Feet (33.5 Meters) | 40 to 60 PSI | 3 to 8 Gallons | Foot valve on the submerged ejector package |
| Centrifugal Booster Pump | 10 Feet (Flooded Suction) | 40 to 70 PSI | 0.5 to 1.5 Gallons | Inline check valve on the suction intake line |
| Submersible Well Pump | Not Applicable (Submerged) | 40 to 60 PSI | None (Self-Priming by design) | Built-in check valve on top of the pump motor |
Troubleshooting Well Pump Priming Failures and Air Leaks
If you have attempted to prime your pump multiple times without success, the system is suffering from a mechanical failure. Use these diagnostic steps to locate and resolve the issue.
Scenario 1: The water poured into the priming port drains away immediately and never fills up.
- Root Cause: A failed, cracked, or debris-clogged foot valve at the bottom of the well pipe. The foot valve is designed to act as a one-way gate, keeping water locked in the vertical pipe when the pump turns off. If it fails, gravity pulls all the water back into the well.
- Actionable Fix: Pull the well drop-pipe out of the well casing. Inspect the brass or plastic foot valve at the end of the pipe. Clean out any sand or mineral crust. If the internal spring or rubber flapper is worn, replace the entire foot valve assembly, re-install the pipe, and repeat the priming process.
Scenario 2: The pump builds pressure temporarily, then drops to zero when the motor stops.
- Root Cause: An air leak in the suction line or a failing inline check valve. Even a microscopic pinhole leak in the suction pipe will allow air to be drawn into the system, breaking the vacuum seal and dropping the water column back into the well.
- Actionable Fix: Inspect all joints and elbow fittings on the suction line between the well head and the pump. Coat the joints with soapy water while the pump is running; look for bubbles or areas where the soapy water is sucked into the pipe. Re-seal any suspect joints with fresh PVC cement or thread sealant.
Scenario 3: The pump motor hums but does not spin, or shuts off due to thermal overload.
- Root Cause: The pump was run dry for too long during previous priming attempts, causing the internal impeller to melt and fuse to the diffuser, or the motor windings have overheated.
- Actionable Fix: Turn off the power immediately. Attempt to manually spin the motor shaft from the rear cooling fan cowl using a flathead screwdriver. If the shaft is locked up, you must disassemble the pump casing to inspect and replace the melted impeller kit, or replace the entire pump unit.
Scenario 4: The pressure gauge fluctuates rapidly, and the pump sounds like it is pumping gravel.
- Root Cause: Cavitation caused by restricted water flow or significant air pockets still trapped in the suction line.
- Actionable Fix: Turn off the power. Open the priming plug and top off the casing with water to purge the residual air pockets. Check for obstructions in the suction line, and ensure the well's water table has not dropped below the level of your foot valve intake.
Frequently Asked Questions
How many times do you have to prime a well pump?
A properly functioning system should prime on the first or second attempt. However, if your suction line is exceptionally long or has multiple horizontal bends, it can take three to four priming cycles to fully purge the air pockets trapped in the high points of the pipe network.
Why does my well pump keep losing its prime?
Frequent loss of prime is almost always caused by a slow leak in the suction piping, a deteriorating foot valve, or a dropping water table that exposes the intake pipe to air. Inspect your fittings for hairline cracks and test the integrity of your check valves.
Can running a well pump dry damage it?
Yes, running a well pump dry will cause severe mechanical damage within minutes. The water flowing through the pump acts as a vital lubricant and cooling agent for the internal rubber seals, shaft packings, and plastic impellers; without water, friction generates intense heat that warps and melts these critical components.
How do I know if my foot valve is bad?
A bad foot valve is indicated if you pour water into the priming port and it drains away instantly, failing to fill the casing. Additionally, if your pump loses prime every time the motor cycles off but runs fine while active, the foot valve is leaking water back into the well.
Do submersible well pumps ever need to be primed?
No, submersible well pumps do not need to be primed because they operate entirely underwater at the bottom of the well. They are constantly flooded with water, meaning air cannot enter the pump intake unless the well's water level drops below the pump itself.
Secure Your Home's Water Supply with Professional Maintenance
If you have followed these priming steps and still cannot restore continuous water pressure, your system may have a deeper mechanical issue or a compromised well casing. Contact a licensed water well professional today to diagnose your system, replace failing components, and protect your home's water supply.
