How to Prime a Well Pump: Step-by-Step Instructions

Why Well Pumps Lose Prime

A well pump "loses prime" when air gets into the system where water should be. Jet pumps and shallow well pumps must maintain a column of water from the pump down to the well water to function. When air breaks this column, the pump spins but can't move water—you'll hear it running but get little or no flow.

Common causes of lost prime include:

• Power outage: After extended outages, water can drain back down, especially if the foot valve is weak
• Failing foot valve: The foot valve at the bottom of the drop pipe prevents water from draining back; when it fails, prime is lost
• Air leaks: Cracks in pipes, loose fittings, or worn pump seals let air into the suction side
• Low water level: If the water table drops below the foot valve, the pump sucks air
• Recent work: Any service that opened the system may have introduced air

Important: Submersible pumps (installed down in the well itself) are self-priming and don't need this procedure. This guide is specifically for jet pumps and other above-ground pumps that require priming.

Tools and Materials Needed

Before you begin, gather these supplies:

• Clean water: Several gallons—5-gallon buckets work well
• Funnel or hose: For directing water into the priming port
• Adjustable wrench or socket set: For the priming plug (usually 3/4" or 1")
• Teflon tape: For resealing the priming plug
• Flashlight: To see inside the pump housing
• Towels or rags: This can get messy

You may also want a helper to add water while you monitor the pump or operate switches.

Step-by-Step Pump Priming Process

Step 1: Turn Off the Power

Go to your electrical panel and turn off the breaker for the well pump. This is typically a 30-40 amp double-pole breaker. Verify the pump won't start by trying the pressure switch or listening for the pump. Never assume it's off—test it.

Step 2: Locate the Priming Plug

Find the priming plug on top of the pump housing. It's usually a square or hex-head plug, often 3/4" or 1". Some pumps have a dedicated priming port; others use a pipe fitting that can be removed. If you can't identify it, check your pump's manual or look for the highest point on the pump casing.

Step 3: Remove the Plug and Check Water Level

Using your wrench, carefully remove the priming plug. Water may spill out if there's still some in the pump. Look inside—if you see the impeller or the housing is dry, the pump definitely needs priming. Set the plug aside and keep the Teflon tape ready.

Step 4: Add Water to the Pump Housing

Using a funnel or hose, slowly pour clean water into the priming port. Fill until water reaches the top of the port. The water will gradually drain down the suction pipe toward the well, displacing air. This process may take several gallons depending on your pipe length and diameter.

Step 5: Cycle the Water

Continue adding water as it drains. You're trying to fill the entire suction line from the pump down to the foot valve. For a 100-foot well with 1-1/4" pipe, this could be 5-10 gallons. Keep adding water until the level holds steady without draining—this means you've displaced all the air.

Step 6: Reinstall the Plug

Once the water level holds, wrap the priming plug threads with fresh Teflon tape (3-4 wraps clockwise). Reinstall the plug and tighten snugly—don't over-tighten as this can crack the fitting.

Step 7: Restore Power and Test

Turn the breaker back on. The pump should start automatically if the pressure tank is low. Listen for normal pump sounds—a smooth hum indicates water is flowing. If the pump runs but makes grinding or whining sounds, shut it off immediately and repeat the priming process.

Step 8: Check for Flow

Open a faucet and verify water flows. It may sputter initially as the last air clears the lines. Within a minute or two, you should have steady flow. If the pump runs but you get no water after 2-3 minutes, turn it off to prevent damage and investigate further.

When Priming Won't Fix the Problem

Sometimes priming doesn't work, or the pump loses prime again shortly after. This usually indicates a more serious issue that requires professional attention:

• Repeated loss of prime within hours or days: Almost certainly an air leak or failed foot valve
• Can't get water to hold in pump: Major leak in suction line, possibly a cracked pipe underground
• Pump makes unusual noises when running: Impeller damage or bearing failure
• Water level in well is too low: Foot valve may be above the water table—the pump can't reach water
• Visible water spraying from pump or pipes: Mechanical failure requiring repair or replacement

If you've attempted priming twice without success, or if the pump keeps losing prime, it's time to call a professional. Continuing to run a pump without proper prime will damage the seals and impeller, turning a minor repair into a major expense.