Well Pump Losing Prime: Causes & Fixes

Symptom-to-Cause Quick Diagnosis

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Cause 1: Air in the System — Re-Prime the Pump First

Before diagnosing deeper issues, the simplest fix for a well pump losing prime is to manually re-prime it. Air can enter the system after power outages, repairs, or periods of no use.

1. Turn off the pump’s circuit breaker and unplug or disconnect power completely.
2. Locate the priming plug on top of the pump housing (usually a 1/4″ or 3/8″ brass plug).
3. Place a bucket under the pump to catch overflow, then remove the priming plug.
4. Slowly pour clean water into the priming port until it fills completely and water is visible at the opening.
5. Replace the priming plug securely, restore power, and turn the pump on immediately.
6. Open a nearby faucet to bleed remaining air from the lines. Water should flow steadily within 60 seconds.
7. If water flows normally, monitor for 24 hours to confirm prime is held.

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Cause 2: Faulty or Worn Foot Valve

The foot valve sits at the bottom of the suction pipe in the well and acts as a one-way check valve, keeping water in the line when the pump is off. A worn or debris-clogged foot valve is one of the most common reasons a pump repeatedly loses prime.

1. After re-priming (Cause 1), shut off the pump and wait 10–15 minutes.
2. Try re-priming again — if the pump has lost prime again within minutes, the foot valve is the likely culprit.
3. Pull the suction pipe from the well (this is a two-person job; secure the pipe safely).
4. Inspect the foot valve screen for debris, sediment, or cracking. Clean or replace as needed.
5. Pour water through the valve from the top — it should flow freely. Pour from the bottom — it should stop completely. If water flows back through, the valve has failed.
6. Thread the new foot valve onto the suction pipe, lower it back into the well, and re-prime the pump.

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Cause 3: Leaking or Cracked Suction Line

Any crack, loose fitting, or pinhole leak on the suction side of the pump allows air to be drawn in, breaking the prime. Even a tiny leak can prevent the pump from maintaining pressure.

1. Shut off power to the pump.
2. Inspect all visible suction-side pipes, unions, and fittings for moisture, mineral staining, or cracks.
3. Run your hand along each joint while a helper briefly turns the pump on — you may feel air being sucked in at the leak point (use caution).
4. Tighten any loose threaded fittings. Wrap joints with PTFE (Teflon) thread tape and re-tighten if leaking persists.
5. Replace any cracked pipe sections using schedule 40 PVC or poly pipe rated for potable water.
6. Pressure-test repaired sections before burying or concealing them.
7. Re-prime the pump after repairs.

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Cause 4: Waterlogged Pressure Tank

A pressure tank with a failed bladder or insufficient air charge can cause the pump to short-cycle and appear to lose prime. The tank can no longer hold enough air pressure to keep water in the system when the pump shuts off.

1. Turn off power to the pump and open a faucet to relieve system pressure.
2. Locate the Schrader valve (like a tire valve) on the top or side of the pressure tank.
3. Press the valve core to check if water sprays out — if it does, the bladder is ruptured and the tank must be replaced.
4. If only air comes out, check the pressure with a tire gauge. It should read 2 PSI below your pump’s cut-in pressure (commonly 28 PSI for a 30/50 switch).
5. If pressure is low, add air with a standard air compressor until the correct charge is reached.
6. Restore power and monitor pump cycling — it should not cycle more than once per minute under normal use.

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Cause 5: Low Water Table or Dry Well

During drought conditions or heavy usage periods, the water level in your well can drop below the foot valve, causing the pump to draw in air and lose prime. This is a seasonal or environmental problem rather than a mechanical failure.

1. Check with your local water authority or neighbors with wells to confirm whether drought or high demand is affecting the area.
2. Review your water usage — back-to-back laundry, irrigation, and showers can temporarily deplete a slow-recharging well.
3. Allow the well to rest for 1–2 hours and then attempt to re-prime and restart the pump.
4. If the problem recurs consistently, have a licensed well driller measure your static water level — you may need the pump lowered deeper into the well.
5. Consider installing a low-water cutoff switch to automatically shut down the pump before it runs dry and overheats.

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Cause 6: Worn Pump Impeller or Shaft Seal

Internal wear to the pump impeller or a failed shaft seal allows water to slip backward inside the pump, making it impossible to maintain prime no matter how many times you re-prime it. This is the most labor-intensive repair and often warrants professional assessment.

1. Shut off power and disconnect the pump from all plumbing.
2. Remove the pump casing bolts and split the casing to expose the impeller.
3. Inspect the impeller vanes for erosion, cracking, or excessive wear — worn vanes will have a rough, pitted surface.
4. Inspect the shaft seal for scoring or cracking; a leaking seal will show moisture around the pump shaft.
5. Replace the impeller and shaft seal as a matched set if either shows damage.
6. Reassemble the pump, re-prime, and test. If performance remains poor, the entire pump body may need replacement.

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Frequently asked questions

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• Well Pump Not Working – Troubleshooting & Repair Guide
• Pressure Tank Waterlogged: Fix Your Well Pump Problems
• Well Pump Short Cycling: Causes & Fixes
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