How To Prime A Well Pump: The Complete Technical Guide For Homeowners

Priming a well pump involves manually filling the pump housing and suction line with water to purge trapped air, enabling the system to create the vacuum pressure necessary for continuous water draw. For shallow well jet systems, this requires securing the electrical supply, opening the priming port, and adding clean water until the chamber is completely filled and pressurized between 30 to 50 PSI. Ensuring an airtight seal on all valves and joints during this process is critical to prevent loss of prime and pump damage.

Unlike submersible pumps that sit directly in the water table and remain naturally primed, surface-mounted pumps—such as shallow well and deep well jet pumps—rely on atmospheric pressure and suction lift to draw water up from the ground. Because air is highly compressible, a pump filled with air cannot create the low-pressure zone required to pull water from the well.

If your system has recently undergone maintenance, suffered a power outage, or experienced a drop in the water table, you must manually prime the pump to restore your water supply. Running a dry pump can warp impellers, destroy mechanical seals, and ruin the motor within minutes.

Pre-Priming Diagnosis and Required Tool Kit

Before attempting to prime your well pump, you must identify the style of your plumbing system and gather the appropriate tools. Working with water systems carries inherent electrical hazards, so preparation and safety are paramount.

Diagnostic Benchmarks

• Shallow Well Jet Pump: Features a single suction pipe running from the well to the pump. Designed for water tables no deeper than 25 feet.
• Deep Well Jet Pump: Features two pipes running from the pump into the well (a suction pipe and a pressure drive pipe). Designed for water tables between 25 and 110 feet deep.
• Target Pressure Range: Standard household systems operate on a 30/50 PSI or 40/60 PSI pressure switch cycle. Your priming goal is to get the pump to hold steady pressure within these thresholds.

Tool, Material, and Resource Checklist

• Pipe Wrench or Channel Lock Pliers: Needed to safely loosen and tighten the heavy-duty metal or plastic priming plug on the pump housing.
• Potable Water Source: 2 to 5 gallons of clean, safe drinking water. If your household water is completely offline, you must source this water from external clean buckets or a neighbor's supply.
• Thread Seal Tape (Teflon): To wrap the priming plug threads upon reinstallation, ensuring an airtight seal.
• Funnel: A clean plastic funnel that fits securely inside the priming port to minimize spillage and prevent dirt from entering the drinking water system.
• Non-Contact Voltage Tester: To verify that the electrical current to the pump is completely severed before starting work.
• Estimated Time Commitment: 30 to 60 minutes, depending on the length of the suction pipe and how many priming cycles are required.
• Project Budget: $10 to $25 (primarily for thread tape, a funnel, and potable water if not already on hand).

Step-by-Step Jet Pump Priming Protocol

Follow this technical procedure precisely to avoid airlocks, seal degradation, or motor burnout.

Step 1: Disconnect the Electrical Power Supply

Working around water and electricity is dangerous. Go to your home's main electrical panel and switch off the dedicated circuit breaker labeled for the well pump.

Warning: Never rely solely on the pump's pressure switch or a local toggle switch to cut power. Always turn off the breaker at the main distribution panel and verify the line is dead using a non-contact voltage tester directly on the pump motor terminals before proceeding.

Step 2: Relieve Residual System Pressure

Open a faucet or a outdoor hose bib situated close to the pressure tank. Let the water run until the flow completely stops and the system pressure gauge reads 0 PSI. This relieves the backpressure on the pump housing, allowing you to safely remove the priming plug without a sudden blowout of pressurized water.

Step 3: Locate and Remove the Priming Plug

Locate the priming port on the top of the pump housing, or "volute" (the cast-iron or plastic casing where water enters and leaves). The priming plug is typically a square or hexagonal bolt head measuring 1/2-inch to 1-inch in diameter.

Using your pipe wrench or channel locks, slowly turn the plug counterclockwise. If the plug is seized due to mineral deposits, apply a small amount of penetrating oil to the threads, wait five minutes, and try again. Wipe away any rust or debris around the opening to prevent contamination.

Step 4: Inspect the Foot Valve and Check Valve

Peer down into the open priming port with a flashlight. In a properly functioning well system, the water you pour down the line should be held in place by a foot valve (a one-way check valve at the very bottom of the pipe inside the well). If you look down the pipe and can see that it is completely dry, or if water drains away instantly when poured, your foot valve may be stuck open or damaged.

Step 5: Fill the Pump and Suction Piping

Place your clean funnel into the priming port. Slowly and steadily pour your clean, potable water into the opening.

Pro-Tip: Pour slowly to allow displaced air to escape out of the same port. If you pour too quickly, you will trap air bubbles inside the impeller chamber, creating a stubborn airlock that will prevent the pump from drawing water even after it is filled.

Continue pouring until the water level rises to the very top of the priming port and remains stable for at least two minutes without dropping. If the water level slowly sinks, it indicates that the air is purging or the foot valve is sealing. Top it off until the level remains completely stationary.

Step 6: Seal the Priming Port

Clean the threads of the priming plug with a wire brush or clean cloth. Wrap the threads with 3 to 4 layers of Teflon tape in a clockwise direction (matching the direction you will turn the plug to tighten it). This ensures the tape does not unwrap as you thread the plug back into the housing.

Thread the plug back into the port by hand to avoid cross-threading, then tighten it firmly with your wrench.

Warning: Do not overtighten the plug, especially if your pump housing is made of plastic or composite materials. Overtightening can crack the housing, necessitating a complete replacement of the pump's wet end.

Step 7: Re-energize the Pump and Monitor Pressure

Close the faucet you opened in Step 2 to allow pressure to build within the system. Turn the main electrical breaker back on.

As soon as power is restored, the pump motor should hum and start running. Watch the built-in pressure gauge closely. Within 30 to 60 seconds, you should see the needle begin to climb steadily away from 0 PSI toward your system's cut-out pressure (typically 50 or 60 PSI).

Step 8: Complete the Prime Cycle

If the pressure rises and the pump automatically shuts off when it reaches its limit, your system is successfully primed. Open a faucet in the house to purge any remaining air spitting from the lines.

If the pump runs for more than two minutes without the pressure gauge moving upward, turn off the power immediately. Running the pump dry for longer than this will overheat the internal shaft seals. If this occurs, wait 15 minutes for the system to cool, remove the plug, and repeat Steps 5 through 7. It is common for deep wells or long horizontal pipe runs to require two or three priming attempts to clear all air pockets.

Well Pump Priming Specifications & Pressure Thresholds

Understanding the technical boundaries of your specific well pump ensures you do not force the system beyond its mechanical limits during the priming and testing phases.

Common Priming Failures & Field Fixes

When a well pump refuses to hold its prime, the issue is almost always related to an air leak or a mechanical failure in the water delivery line. Use these troubleshooting steps to diagnose and repair the issue.

Scenario 1: The water level in the priming port drops rapidly during filling.

• Root Cause: The foot valve at the bottom of the well pipe is stuck open, damaged, or clogged with silt, allowing the priming water to drain back down into the well aquifer.
• Actionable Fix: You must pull the drop pipe out of the well casing to access the foot valve. Inspect the spring-loaded valve mechanism. Clean out any sand, sediment, or mineral scaling. If the rubber seal is cracked or the spring is broken, replace the entire foot valve assembly.

Scenario 2: The pump motor runs, but the pressure gauge hovers near zero without climbing.

• Root Cause: A micro-leak in the suction line is letting air into the system. Because air is drawn in more easily than water, the pump cannot create a strong enough vacuum.
• Actionable Fix: Turn off the power. Inspect every joint, elbow, and coupling on the suction pipe. Brush a thick mixture of dish soap and water over the joints; when the pump is briefly turned on, look for bubbles or signs of suction. Re-seal leaking joints with pipe dope or Teflon tape.

Scenario 3: The pump primes successfully but loses pressure overnight.

• Root Cause: A slow leak in the check valve near the pressure tank, or a failing foot valve that is slowly letting water slip back into the well under static pressure.
• Actionable Fix: Install an auxiliary, spring-loaded check valve on the suction line immediately before the pump inlet. This acts as a secondary barrier, holding the water column in the pump head even if the primary foot valve has a minor leak.

Scenario 4: The pump works for a few minutes, then spits air and loses prime.

• Root Cause: The water table in the well has dropped below the level of the foot valve or intake screen, causing the pump to draw in air alongside water.
• Actionable Fix: Measure the draw-down level of your well. If the water table has receded, you will need to add more drop pipe to lower the foot valve deeper into the well, ensuring it remains submerged during peak pumping hours.

Frequently Asked Questions

Can you ruin a well pump by running it without priming?

Yes, running a centrifugal or jet pump dry will quickly ruin it. The water inside the pump housing acts as a coolant and lubricant for the mechanical shaft seal and internal impellers. Operating the motor without water causes rapid heat buildup from friction, warping plastic internal components and destroying the seals within two minutes.

How many times do you have to prime a well pump before it works?

While a perfectly sealed system can be primed in a single attempt, it is common to require two to four attempts. This is especially true if the suction line is long or has horizontal runs, as air pockets can easily become trapped in high spots along the pipe and must be slowly worked out.

How do I know if my well pump has lost its prime?

The most obvious indicators are a total lack of water flow at your household faucets, a pressure gauge on your tank reading 0 PSI, and a pump motor that runs continuously without shutting off. You may also hear a dry, metallic humming sound from the pump motor rather than the usual wet, rushing sound.

Why does my well pump keep losing its prime?

Recurring loss of prime is almost always caused by a tiny air leak in the suction line piping, a failing check valve, or a leaking foot valve. Even a pinhole leak in a joint can draw in enough air to break the hydraulic vacuum when the pump shuts down, causing the water to drain back into the well.

Professional Diagnostics and System Maintenance

If your well pump continues to lose its prime after multiple attempts, there may be an underground pipe fracture or a deep-well mechanical failure. Contact a licensed water system technician to perform a professional pressure test and restore your water supply safely.