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Pump will not prime

Pump Won’t Prime

Why Your Pool Pump Won’t Catch Prime & How to Fix It

If your pool pump won’t prime—or loses prime after running—it means the pump is not able to pull and hold water. Priming is essential for the system to run correctly. Without proper prime, the pump can overheat, fail to circulate water, and may damage the motor.

This guide covers the most common causes and what you can check before requesting service.


⭐ 1. Water Level Too Low (Most Common)

Your pump needs a constant supply of water from the skimmer.

If the pool water level is low, the pump will pull air instead of water.

Signs:

✔ Pump basket won’t fill

✔ Bubbles in return jets

✔ Skimmer making a slurping sound

Fix:

  • Raise the water level to mid-skimmer (halfway up the opening)
  • Make sure the skimmer weir door is moving freely


⭐ 2. Pump Lid O-Ring Not Sealing

If the pump lid O-ring has even a tiny leak, the pump will pull air instead of water.

Check for:

✔ Dry O-ring

✔ Cracked or flattened O-ring

✔ Debris in the lid groove

✔ Lid not tightened fully

Fix:

  1. Turn off the pump
  2. Remove the lid
  3. Clean O-ring and pump lid seat
  4. Apply silicone lubricant
  5. Reinstall and tighten

A bad O-ring is the #1 cause of priming failure.


⭐ 3. Clogged Skimmer or Pump Basket

If water flow is blocked, the pump cannot catch prime.

Check:

✔ Skimmer baskets full

✔ Pump basket packed with debris

✔ Debris stuck around impeller intake

✔ Skimmer socks full

Fix:

  • Clean all baskets
  • Rinse out pump housing
  • If debris entered the impeller, the pump may need to be disassembled


⭐ 4. Air Leak on Suction Side

Any leak on the suction side (from the skimmer to the pump) will cause the pump to suck air instead of water.

Possible leak points:

  • Pump lid O-ring
  • Pump union O-rings
  • Cracked PVC fittings
  • Loose unions
  • Suction valves
  • Vacuum hose

Signs:

✔ Excessive bubbles

✔ Pump fills and drains repeatedly

✔ Air visible under pump lid

Fix:

  • Tighten unions
  • Inspect for visible cracks
  • Ensure valve handles are fully sealed
  • Replace faulty O-rings

If the leak is underground, professional diagnosis is needed.


⭐ 5. Pump Speed Too Low (Variable Speed Pumps)

A VS pump running too slowly may not have enough suction to prime itself.

Fix:

  • Increase speed to 2,800–3,450 RPM during priming
  • After prime is established, reduce to normal running speed


⭐ 6. Blocked or Dirty Filter

If filter pressure is very high, water cannot move through the system.

Fix:

  • Clean cartridge
  • Backwash sand or DE filter
  • Reset to normal pressure

High pressure = low flow = poor priming.


⭐ 7. Suction Valve Position Incorrect

Valves must be positioned to allow full suction from the pool.

Check:

✔ Valve partially closed

✔ Wrong suction port selected

✔ Vacuum line open

✔ Spa suction selected instead of pool

Fix:

  • Ensure valve lines up correctly with the port
  • Set valve fully to POOL when priming
  • Close vacuum line if not in use


⭐ 8. Pump Above Water Level (Lift Too High)

If the pump sits too far above the water level (common on older pads or raised equipment areas), priming becomes harder.

Fix:

  • Use a higher priming RPM
  • Ensure all suction lines are sealed
  • Improve water flow by lowering pump or adjusting plumbing (if possible)


⭐ 9. Impeller Blockage

Small debris can enter the pump and clog the impeller.

Signs:

✔ Weak flow

✔ Pump makes a quiet humming noise

✔ Basket fills slowly

Fix:

Pump must be opened and cleaned—often requires service.


⭐ 10. When to Contact Professional Pool Company

You should call us if:

✔ Pump will not prime no matter what

✔ Water enters the pump and immediately drains back out

✔ Pump gets hot quickly or shuts off

✔ Visible leaks at pump inlet

✔ Pump runs loud or vibrates

✔ Flow decreases over time

We can diagnose:

  • Suction leaks
  • Impeller blockages
  • Bad pump seals
  • Plumbing issues
  • Undersized or aging pumps


⭐ Summary

A pump that won’t prime is usually caused by:

  • Low water level
  • Pump lid O-ring leak
  • Blocked baskets
  • Suction-side air leak
  • Low RPM
  • Valve misalignment
  • Dirty filter
  • Impeller blockage

Most priming issues can be resolved with simple checks.


⭐ Need Help?

If your pump still will not prime after these steps, contact Professional Pool Company. We’ll identify the cause and restore full system flow.

Updated on: 29/11/2025

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