How to Prime a Well Pump (Step-by-Step)

Pour clean water into the pump’s priming port until it overflows, reseal the port, restore power, and let the pump run until the pressure gauge climbs to cut-in pressure (typically 30 PSI). If pressure never builds after 60 seconds, you have a secondary problem: a failed foot valve, an air leak, or an undersized pump.

plumber installing well pump and pressure tank in residential basement

That procedure sounds simple, but there’s an important distinction most guides skip: only jet pumps lose prime. Submersible pumps sit underwater and are self-priming by design. If yours has no water, the problem is a failed motor, check valve, or wiring issue, not a lost prime.

Quick answer

Check this before priming your pump: ensure there’s no air in the lines to avoid the impellers spinning fruitlessly. Failure to do so means the pump loses prime and trips the breaker, producing nothing but wasted electricity and a running dry tank.

You need to prime a jet pump when:

The system ran dry (pressure dropped to zero and the pump ran without water)
Power was cut for an extended period and water drained back
The pump was recently replaced or disconnected
A suction line fitting was opened for any reason

You do not need to prime a submersible pump. Submersible pumps can’t lose their prime; they’re submerged in water by design. If a submersible has no water flow, something else has failed. See our well pump repair troubleshooting guide for that scenario.

Is this guide for you?

you have an above-ground jet pump (typically in a basement, pump house, or utility room), your pump is running but producing no water or low pressure, you recently serviced the pump and need to restore water flow, or you had a power outage and lost water pressure.

Skip this guide if your pump is a submersible (underground, in the well casing), since submersibles don’t lose prime. Also skip it if you need to prime a brand-new submersible installation. That’s covered in our how to install a well pump guide.

What you’ll need

Gather these before starting. You don’t want to pause mid-procedure:

Clean water: at least 2 gallons. Tap water from a neighbor or stored water works fine.
Pipe wrench or adjustable wrench: to remove the priming plug.
Teflon tape: to reseal the plug threads.
Non-contact voltage tester: to confirm power is off before touching any fittings.
Pressure gauge (if your system doesn’t already have one): to verify cut-in pressure after priming.

Video guide

Video: “WELL PUMP NOT PRIMING? HERE’S WHAT TO CHECK FIRST!” by PLUMBING WITH TIM

Step-by-step: how to prime a jet pump

Time: 20–45 minutes. Difficulty: Moderate.

Cut power at the breaker. Locate the dedicated circuit breaker for the pump and switch it off. Verify it’s off with a non-contact voltage tester before touching any fittings. Jet pump motors are hardwired, and a shock in a wet environment is serious.
Find the priming plug. On most residential jet pumps, it’s a large hex bolt or pipe plug on the top of the pump casing, usually brass or plastic. Check both the top and the front of the pump housing if you don’t see it immediately.
Remove the priming plug. Use a pipe wrench for a tight plug. Have a rag in your other hand, since residual water will drip out when the plug comes free. That’s normal.
Pour water into the priming port slowly. Use a funnel if the port is small. Pour in about 1 gallon and wait 30 seconds. The water is filling the suction line that runs from the pump down to the well. When the line is full, water will no longer drain down and the port will stay full. Add water until the port is full and stays full, typically 1.5-2 gallons for a standard residential system.
Reseal the priming plug. Wrap 3–4 turns of Teflon tape around the plug threads before reinserting. Hand-tighten, then snug with the wrench. Don’t over-torque plastic plugs.
Restore power. Flip the breaker back on. Stand at the pressure gauge and watch.
Monitor the pressure gauge. Within 30–60 seconds, the gauge needle should begin rising. A primed pump reaches cut-in pressure (typically 30 PSI) in under a minute. The pressure switch will cut the pump off at cut-out pressure (typically 50 PSI).
Open a faucet to bleed trapped air. Even with a good prime, some air remains in the lines. Expect sputtering and spitting for 1–2 minutes before steady flow. This is normal.

After the first successful pressure cycle, we recommend running water at a faucet for 5 minutes to flush any sediment that may have entered during the dry-run period.

Why the pump won’t hold its prime

If you go through the procedure and the pump loses prime again within minutes or hours, you have a secondary problem:

Same idea.

A foot valve failure often causes issues. Positioned at the suction line’s end, it prevents water from flowing backward when the pump is inactive. Its malfunction leads to continuous water draining back down the line whenever the pump stops. This results in a brief prime that rapidly diminishes. Replacing the foot valve necessitates access to the suction line, typically requiring a plumber or well driller. Expect parts to cost between $15 and $40, with labor making up most of the expense.

An air leak in the suction line is another possibility. A cracked fitting, a loose union, or a failed O-ring allows air to enter the line. This creates a partial prime that builds pressure slowly but never reaches cut-out. Run your hand along all suction fittings while the pump is running. A slight hiss or vibration at a joint points to the leak location.

Cracked suction pipe is more common in older systems or those in areas with hard winters, where frozen ground can crack buried pipe. If all above-ground fittings are solid and the pump still won’t hold prime, a broken pipe is possible.

Nothing fancy.

If the pump runs and you can hear it spinning but pressure barely moves, the impeller may be worn. That’s not a priming problem; it’s a pump failure.

When to call a professional

We recommend calling a licensed plumber or well service company when:

Pay attention.

The pump won’t hold prime after 2 attempts. Foot valve and suction line issues require access you may not have.
The circuit breaker trips when you restore power. That signals a motor fault that gets worse with repeated resets.
No pressure builds at all after priming. The pump may be too small, or the well’s yield has dropped.
The repair requires in-well work. Anything inside the well casing, including a deep foot valve, should be handled by a licensed well driller in most states.

If the diagnosis points to a pump that needs full replacement, see our cost to replace a well pump guide to understand what you’ll be spending before calling a contractor.

FAQ

How long does it take to prime a well pump?

The physical procedure takes 15–20 minutes. After restoring power, expect another 1–3 minutes for the pump to reach full pressure and for air to bleed from the lines. If it takes longer than 5 minutes without reaching cut-in pressure (30 PSI), something else is wrong.

Why does my well pump keep losing its prime?

A pump that repeatedly loses prime almost always has a failed foot valve, the one-way check valve at the bottom of the suction line. When the foot valve fails, water drains back down the line every time the pump stops. The pump loses its prime as a result. Foot valve replacement is a relatively low-cost repair ($15–$40 in parts) but requires access to the suction line.

Can a submersible pump lose its prime?

No. Submersible pumps are always submerged in water and can’t lose prime. If a submersible pump has no water flow, the issue is a failed motor, broken check valve, wiring fault, or pressure switch problem. Not lost prime. See our pressure switch replacement guide if the motor runs but pressure never builds.

How much water does it take to prime a well pump?

Most residential jet pump systems require 1.5–2 gallons of water to fully fill the suction line and pump housing. Larger systems with longer suction runs (over 20 feet) may need 3 gallons. Pour slowly and watch for the port to stay full. That’s your indicator the line is primed.

What PSI should my pressure tank be after priming?

When your pump cycles from its lower setting, say 40 PSI, to the higher one around 60 PSI under a 40/60 pressure setup, ensure the bladder in the pressure tank has an initial air charge of 38 PSI. Use any reliable tire gauge and locate the Schrader valve atop the tank to confirm this critical setting.

For a complete overview of well pump installation and costs, visit our well pump installation cost guide.

Check this before you head out to replace that pump; if it’s failing and won’t start, it could be down to a low PSI rating. Ensure the tank is not running dry or losing prime, as this can trip the breaker too. You’ll want to verify your pump’s psi, often rated around 40-60 psi, isn’t too low. If the issue persists, the problem might lie with your pressure switch; check for faulty contacts that won’t close properly when the tank runs dry. On a related note, if you suspect your pump isn’t starting due to electrical issues, it’s wise to test connections and replace any worn wiring, as faulty cables can drain performance just like a plugged drain stops up water flow. With a bit of probing, you should be able to pinpoint what’s amiss in no time at all. Don’t overlook the basics: a failing pump often costs more than a replacement switch or some new wires.