Pool pump not priming or losing prime: how to fix it

Common symptoms

• The motor runs, but the strainer pot stays empty or only half fills with water.
• Air bubbles swirl in the pot under the clear lid.
• Bubbles spit out of the return jets in the pool wall.
• The pump primes, then loses it after a few minutes or overnight.
• Flow at the returns is weak, and the filter gauge reads lower than usual.
• The pump sounds louder or rattly.

Quick checks before anything else

• Pool water is at least halfway up the skimmer opening.
• Every suction and return valve is open.
• The skimmer basket and the pump basket are empty and not cracked.
• The strainer pot is filled with water before you start the pump.
• The lid O-ring is clean, lubricated, sitting in its groove, and the lid is hand-tight.
• The air relief valve on top of the filter is open when you start the pump.
• Both drain plugs are back in the pump if it was winterized.

What makes a pool pump lose prime?

Prime means the pump and the suction pipe are full of water, so the pump can pull more water behind it. A self-priming pump can lift water from below, but only when the pot starts full and no air gets in. Hayward puts it plainly: any self-priming pump will not prime if there are suction air leaks.

• Lid O-ring leak A dry, cracked or twisted O-ring, or one dirt grain on the seat, lets air in at the top of the pot. This is the first thing Hayward checks.
• Suction-side air leak Loose unions, threaded fittings, valve stems or drain plugs before the pump. The sign is bubbles at the return jets.
• Low water level The skimmer gulps air once the water drops too low. Pentair warns the pump then loses prime and runs dry.
• Clog A packed skimmer or pump basket, a blocked suction line, or debris in the impeller starves the pump of water.
• Not enough water to start An empty pot, or a pump mounted more than about 10 feet above the water.
• Priming setting too low On variable-speed pumps, a priming speed or time set too low for your plumbing.

Step-by-step: getting a pool pump to prime and stay primed

We go from the free checks to the ones that need a gauge or a pro. Turn the pump off at the breaker before you open anything.

1. Raise the water level. Pentair says to keep the water about halfway up the skimmer opening. If it falls below, the skimmer pulls air, the pump loses prime and runs dry, and the shaft seal gets damaged. Top the pool up with a garden hose before you try again.
2. Open every valve. Hayward says all suction and return valves must be open while the pump runs, and the filter valve must be set to send water back to the pool. Only change valve positions with the pump off.
3. Empty both baskets. Clean the skimmer basket, then the basket in the pump pot. Hayward says not to strike the basket to clean it. On Pentair pumps, line up the notch in the bottom of the basket with the rib in the pot when you put it back. Replace a cracked basket.
4. Fill the pot and seal the lid. Hayward’s routine: stop the pump, close the valves, release pressure at the filter’s air relief valve, take off the lid, and fill the pot with water up to the suction pipe. Clean the O-ring, check it for cracks, lube it with the lubricant your manual names (Hayward specifies Jack’s 327), and seat it in its groove. Tighten the lid by hand only. If it is stuck, see pool pump lid won’t open.
5. Start it the safe way. Open the valves again and open the air relief valve on top of the filter. Hayward says to stand at least 10 feet from the pump and filter at startup. When a steady stream of water, not air or spitting air and water, comes out of the air relief valve, close it.
6. Give it time, but not too much. Hayward says its Super Pump can take up to 10 minutes to prime, but if it has not primed in 5, stop the motor and find the cause. Priming time grows with the height and length of the suction pipe. See the table below for other models. Never let it run dry for long: water cools and lubricates the shaft seal.
7. Hunt for suction air leaks. Bubbles at the return jets mean air is getting in before the pump, per Hayward. Check every union, threaded fitting, valve stem and drain plug between the skimmer and the pump, and any hose clamps. Hayward’s fixes: tighten unions, reseal threaded joints with PTFE tape, and repair or replace valves whose O-rings or packing glands (the seals around the valve handle stem) leak.
8. Test the suction for a clog. With the skimmer full and the pump running, take out the skimmer basket and hold a flat object over the bottom port, as Hayward’s Super Pump VS manual describes. If you feel no pull, the line may be blocked. A pool tech can confirm with a vacuum gauge at the strainer lid: Hayward expects 5 to 6 inches of vacuum. Hayward sends a clogged suction line to a qualified pro.
9. Check the impeller. If the pot has water but the pump will not pull a vacuum, Hayward says to check for debris in the impeller and confirm the motor is getting full voltage. A jammed or clogged impeller also shows up as a pump that hums; see pool pump humming but not running.
10. Adjust variable-speed priming. Pentair’s IntelliFlo3 troubleshooting lists “priming speed or range too low” and says to adjust the priming settings until the pump primes every time. On the Hayward Super Pump VS, you can set priming at maximum speed for 0 to 15 minutes in 30-second steps.
11. Check the pump height and speed. Hayward’s two-speed motors only self-prime on high speed, so start them on high. If your pump sits more than 10 feet above the water, it is outside what Hayward, Pentair and Jandy list for their pumps.

Hayward vs Pentair vs Jandy: priming numbers

The method is the same on all three brands, but the limits differ, so check the manual for your model.

Pentair adds one rule for pumps below the pool’s water level: close the suction and return lines before you open the pot, and open them again before you start. For the rest of the pump system, see our pool pump problems hub.

When to call a pool or spa pro

• You see bubbles at the returns but cannot find the leak at any fitting you can reach.
• The skimmer test shows no suction, which points to a blocked suction line.
• The pump primes only when someone holds a hose in the skimmer.
• Water drips under the pump between the motor and the pump body (a worn shaft seal).
• The pump ran dry for a long time and now leaks or squeals.

Common questions