SC By SCWS Team | February 2, 2026 | 10 min read
How to Prime a Well Pump
Lost water pressure and your jet pump won't start pumping? You likely need to prime it. Priming a well pump is one of the most common DIY fixes for jet pump systems, but it must be done correctly to avoid damaging your equipment. This guide walks you through the complete process, explains when priming is necessary, and helps you troubleshoot if your pump won't prime.
⚠️ Important: Does Your Pump Need Priming?
- • Jet pumps (above ground): YES - both shallow and deep well types need priming
- • Submersible pumps (in the well): NO - they don't require priming
- • Not sure which you have? If your pump is in a pump house or garage, it's a jet pump
What Does Priming a Well Pump Mean?
Priming means filling the pump housing and suction pipe with water before operating. Well pumps work by creating suction to draw water up from the well, but they can only create suction in water—not in air. If air gets into the pump or suction line, the pump loses its ability to draw water and "loses prime."
Think of it like drinking through a straw. If the straw is full of liquid, you can easily sip. But if there's an air gap, you're just sucking air. Your jet pump works the same way—it needs an unbroken column of water from the well to the pump to function.
When You Need to Prime Your Pump
Common situations that require priming:
New Installation
Any newly installed jet pump must be primed before first use
After Repairs
Any work that opened the suction line or pump housing requires re-priming
Extended Non-Use
If a vacation home pump sat unused for months, it may have lost prime
Power Outage Recovery
Sometimes water drains back during extended outages
Foot Valve Leak
A failing check valve at the bottom of the well allows water to drain back
Air Leak in System
A loose fitting or crack allows air into the suction line
What You'll Need
Gather these supplies before starting:
Supplies and Tools
Supplies:
- Clean water (3-5 gallons minimum)
- Funnel or large pitcher
- Teflon tape (if priming plug needs resealing)
- Rags or towels
- Bucket to catch spillage
Tools:
- Adjustable wrench or pliers
- Screwdriver (if pump has priming cap)
- Flashlight (for inspection)
- Garden hose (for continuous filling method)
🚨 Safety First
Always turn off electrical power to the pump before working on it. Verify power is off by checking that the pump doesn't run when pressure drops. Lock out the breaker if possible to prevent someone from accidentally turning it on while you're working.
Step-by-Step: Priming a Shallow Well Jet Pump
Shallow well jet pumps are the most common type that requires priming. They have a single pipe going into the well and the pump sits above ground.
Step 1: Turn Off Power
Go to your electrical panel and switch off the breaker for the well pump. This is typically a 240V double breaker labeled "Well Pump" or similar. Verify it's off—the pump should not run even when pressure is low.
Step 2: Locate the Priming Port
Look on top of the pump housing for the priming plug or port. It's usually:
- A square or hex-head plug that unscrews
- A threaded cap with a rubber gasket
- Located on the volute (snail-shell-shaped) part of the pump
- Sometimes combined with a pressure gauge fitting
Step 3: Remove the Priming Plug
Use an adjustable wrench to carefully remove the priming plug. Turn counterclockwise. There may be a small amount of water remaining in the pump that will leak out—have a rag ready. Inspect the plug for damage and set it aside.
Step 4: Pour Water Into the Pump
Using a funnel or pitcher, slowly pour clean water into the priming port:
- Pour slowly to allow air to escape and water to fill all cavities
- You may hear gurgling as air is displaced—this is normal
- Continue until water reaches the top of the port and stays there
- If water immediately drains down, you have a foot valve problem (see troubleshooting)
Step 5: Let Water Settle
Wait 1-2 minutes after filling. Water needs to flow down the suction pipe and fill it completely. Add more water if the level drops. Repeat until water stays at the top of the priming port without draining.
Step 6: Replace the Priming Plug
Once water stays at the top:
- Wrap the plug threads with fresh Teflon tape (clockwise when looking at threads)
- Thread the plug in by hand first to avoid cross-threading
- Tighten firmly with wrench—snug but not over-tight
- A small leak here will cause the pump to lose prime again
Step 7: Restore Power and Test
Turn the breaker back on. The pump may start immediately if pressure is low, or you can trigger it by opening a faucet:
- Listen for the pump to start running
- Within 30-60 seconds, water should start flowing from the open faucet
- Watch the pressure gauge climb toward cut-off pressure
- If no water flows after 2 minutes, turn off power and repeat the process
✅ Success Signs
You'll know priming was successful when: water flows steadily from faucets, the pressure gauge shows increasing pressure, the pump eventually shuts off at cut-out pressure, and the system maintains pressure when idle.
Priming a Deep Well Jet Pump
Deep well jet pumps have two pipes going into the well and use a jet assembly down-hole to help lift water from greater depths (typically 25-110 feet). The priming process is similar but requires more water and patience.
Key Differences for Deep Well Pumps
- More water needed: 3-5 gallons or more to fill longer suction lines
- Longer settling time: Water must travel further down the well
- Two pipes to fill: Both pressure and suction lines need water
- May need repeated priming: Deep wells often require 2-3 attempts
Follow the same steps as shallow well priming, but be prepared to add significantly more water and repeat the process multiple times. For very deep wells, the continuous fill method (described below) often works better.
Alternative Method: Continuous Fill Priming
For stubborn pumps or deep wells, this method provides continuous water supply:
Continuous Fill Method
- Connect a garden hose to a working water source (neighbor's house, water storage tank, or city water if available)
- Position the hose to pour into the priming port
- Turn on the water supply to provide a slow, steady stream
- Let water run for several minutes to ensure complete filling
- Turn on pump power while water is still flowing into priming port
- Once pump catches and starts pumping on its own, turn off hose and replace plug
This method works well because it maintains water supply even as the suction line draws water down, giving the pump the best chance to establish suction.
Troubleshooting: When Your Pump Won't Prime
If you've tried priming several times without success, one of these issues is likely the cause:
Problem: Water Drains Out Immediately
Likely Cause: Failed foot valve (check valve at bottom of well)
Solution: The foot valve needs to be replaced. This is a professional job requiring pulling the pipe from the well.
Problem: Water Level Drops Slowly During Priming
Likely Cause: Air leak in suction line or fittings
Solution: Inspect all fittings on the suction side for cracks or loose connections. Tighten and re-seal with Teflon tape or pipe dope. Check for cracks in the pipe.
Problem: Pump Runs But No Water Comes Out
Likely Causes: Pump not fully primed, clogged impeller, or worn impeller
Solution: Try priming again with more water. If that fails, the pump may need internal cleaning or repair.
Problem: Pump Primes But Loses Prime Overnight
Likely Cause: Slow leak in foot valve or suction line
Solution: The system has a small leak allowing water to drain back. Check all connections; foot valve likely needs replacement.
Problem: Water Spurts Then Stops
Likely Cause: Air pockets in the line or partially clogged foot valve
Solution: Try priming with the continuous fill method. If that fails, the foot valve screen may be clogged with debris.
Understanding Your Foot Valve
The foot valve (also called a check valve) is critical to maintaining prime. It's located at the bottom of the suction pipe inside the well and serves two purposes:
- Keeps water in the pipe: When the pump stops, the valve closes to prevent water from draining back down
- Filters debris: Most foot valves include a screen to keep sand and debris out of the system
Foot valves wear out over time, especially in sandy wells or with high mineral content. Signs of a failing foot valve include:
- Needing to re-prime frequently
- No water first thing in the morning (drains overnight)
- Water drains immediately when trying to prime
- Pump takes longer to build pressure after sitting idle
Replacing a foot valve requires pulling the suction pipe from the well—generally a job for a professional with the right equipment.
Preventing Future Priming Problems
Once your pump is working, these practices help prevent losing prime:
Prevention Tips
- ✓ Maintain tight connections: Periodically check fittings on the suction side for tightness
- ✓ Protect from freezing: Insulate pump houses and pipes in cold weather
- ✓ Run pump occasionally: If property sits unused, run the pump monthly to keep seals moist
- ✓ Monitor water levels: Low well levels can cause air to enter the system
- ✓ Address small issues quickly: A small leak becomes a big problem if ignored
When to Call a Professional
While priming is a straightforward DIY task, some situations require professional help:
- Pump won't prime after multiple attempts
- Water drains back immediately (foot valve replacement needed)
- You suspect air leaks but can't locate them
- Pump motor sounds unusual or won't run
- System requires priming more than a few times per year
- You have a submersible pump (priming isn't the issue)
- You're uncomfortable working around electrical equipment
Our technicians diagnose and repair pump problems quickly. Learn more about our well pump repair services.
Frequently Asked Questions
What does it mean to prime a well pump?
Priming a well pump means filling the pump housing and suction line with water to remove air. Well pumps cannot pump air—they need water inside to create suction. Without priming, the pump runs dry and cannot draw water from the well.
Do all well pumps need to be primed?
No. Submersible pumps don't need priming because they're installed underwater in the well. Only jet pumps (shallow well and deep well) and above-ground centrifugal pumps require priming. If you have a submersible pump and lost water, the issue isn't priming—it's likely a pump failure or water level problem.
Why won't my well pump prime?
Common reasons include: air leak in suction line or fittings, damaged foot valve not holding water, cracked pump housing, suction line too long or too high, clogged foot valve screen, low water level in well, or worn pump impeller. Check all connections and the foot valve first.
How long should it take to prime a well pump?
A properly functioning pump should prime within 1-2 minutes after filling with water. If the pump runs longer than 5 minutes without producing water, turn it off to prevent damage. Check for air leaks, foot valve problems, or insufficient water in the priming process.
Can I damage my well pump by running it without priming?
Yes. Running a jet pump dry (without water) causes severe damage quickly. The water acts as a coolant and lubricant for seals and bearings. Dry running for even a few minutes can destroy seals, warp impellers, and burn out the motor. Always ensure proper priming before running.
How much water do I need to prime a well pump?
Typically 1-2 gallons for shallow well jet pumps, and 2-5 gallons for deep well jet pumps (which have longer suction lines to fill). Have at least 5 gallons of clean water available—you may need to repeat the process. Use potable water, not dirty or contaminated water.
Pump Still Won't Prime? We Can Help
If you've tried priming your jet pump without success, there may be an underlying issue with your foot valve, suction line, or pump itself. Our technicians can diagnose the problem and get your water flowing again. We service all types of well pumps throughout San Diego County.
