The pump is running. You can hear it. But the basket is half empty, no water is coming back into the pool, and the motor is starting to whine.
That pump has lost its prime. It is spinning against air instead of water, and air does not cool it. Shut it off before you read the rest of this.
Why priming matters
A pool pump cannot pull air out of a pipe the way it pulls water. It needs water already sitting in the housing to grab onto.
Run it dry and the shaft seal cooks in minutes. That is a repair, not a chore.
Check the water level before anything else
Walk to the pool and look at the skimmer. The water should sit halfway up the opening.
Low water lets the skimmer gulp air, and the pump loses prime every time. Fill the pool first, because the rest of this is wasted effort otherwise.
Prime it
Turn the pump off at the breaker. If you have a multiport valve, set it to FILTER.
Open the air relief valve on top of the filter and leave it open.
Twist the clear pump lid off and lift the basket out. Clean the leaves out of it, because a packed basket starves the pump on its own.
Now fill the pump housing with water from a hose. Keep going until it overflows. Put the basket back and fill it again.
Look at the lid o-ring before you close it. It should be soft and clean. Wipe it, and rub a little silicone lubricant on it, never petroleum jelly.
Hand tighten the lid. Do not put a wrench on it.
Turn the breaker on. Water should start moving within 30 seconds. When steady water comes out of the air relief valve, close it.
If nothing happens in two minutes, shut it off and fill again. Some pumps take three tries.
When priming does not hold
You got it primed and it lost the prime again by morning. Now you are chasing an air leak on the suction side, which is everything between the pool and the pump.
Look for these.
- Air bubbles coming out of the return jets in the pool.
- A pump basket that never stays full while running.
- A cracked or flat pump lid o-ring.
- A cracked pump lid, which is common after years of Texas sun.
- A loose drain plug on the bottom of the pump.
- A leaking pipe union at the pump inlet.
Here is the tricky part. A suction leak sucks air in, so it usually leaves no puddle. Water leaks show up on the pad. Air leaks hide.
One trick works well. With the pump running, spray a little shaving cream around each joint. Where the cream gets pulled in, that is your leak.
Things people get wrong
Do not crank the lid with a tool. Overtightening deforms the o-ring and creates the exact leak you are trying to stop.
Do not use petroleum jelly on the o-ring. It swells the rubber and ruins it.
Do not keep restarting a pump that will not catch. Each dry run costs you more of that seal.
When to call instead
Some of this is not a homeowner job. Stop right there if the motor hums but will not spin. Stop if it trips the breaker or smells like burning. Stop if it screams even after it catches water.
A screech usually means bearings. A trip usually means electrical. Our guide to common pool pump repairs covers what each sound points to.
And if the water level keeps dropping on its own, the prime is a symptom. Check evaporation against a real leak before you replace anything.
We have serviced pools in Victoria since 1968, and our repair techs are Texas RAIL licensed. Call (361) 575-5821.
Frequently Asked Questions
How do you prime a pool pump?
Shut the power off, open the air relief valve on the filter, take the pump lid off, and fill the pump housing with a hose until it overflows. Put the basket and lid back on hand tight, then turn the power on. Close the relief valve once steady water comes out.
How long does it take a pool pump to prime?
Usually 30 seconds to two minutes. If no water is moving after two minutes, shut it off and fill the housing again. Never let it run dry while you wait.
Why does my pool pump keep losing prime?
Air is getting in somewhere between the pool and the pump. The usual causes are a low water level, a clogged skimmer or pump basket, a worn pump lid o-ring, a cracked lid, or a loose drain plug.
Can running a pool pump dry damage it?
Yes, and fast. Water cools the shaft seal. Without it the seal can fail in a few minutes, and the motor can follow.
What do air bubbles in the return jets mean?
They mean the pump is pulling air. Check the water level at the skimmer first, then the pump lid o-ring and the pipe unions at the pump.
Should I grease the pump lid o-ring?
Yes, with silicone lubricant only. Petroleum jelly swells the rubber and ruins the seal.
