How to Prime a Pool Pump (and What to Do When It Won’t Prime)
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Key takeaways
- Priming means filling the pump housing and suction line with water so the impeller has something to push. A pump cannot move air.
- The short version: power off, open the air relief valve, fill the pump basket with a hose, seal the lid, power on, and close the relief valve once water spits out.
- Most pumps catch prime within 1 to 3 minutes. If yours has not caught it in 5, shut it off. Running dry can ruin the shaft seal in minutes.
- When a pump will not prime, it is almost always one of three things: low water, a clog, or an air leak on the suction side.
Every in-ground pool pump sits above the water line at least some of the time, which means it has to pull water up to itself before it can circulate anything. After a cleaning, a winter shutdown, a power outage or a repair, that column of water drains back and the pump has to be primed again. Done right it takes five minutes. Done wrong, a dry-running pump melts its seal and you are looking at a repair bill instead of a hose.
Before you start
- Turn the pump off at the breaker or timer. Do not rely on the pump’s own switch while your hands are in the basket.
- Check the water level. It should sit about halfway up the skimmer opening. Below a third and the skimmer gulps air, and no amount of priming will hold.
- Grab a garden hose and, if the lid o-ring looks dry, a tube of silicone-based o-ring lubricant (never petroleum jelly, which swells rubber).
How to prime an in-ground pool pump, step by step
- Set the valves. Put a multiport filter valve on “Filter”. Open the skimmer and main drain valves. If you have one stubborn line, prime on the skimmer alone first, then open the drain.
- Open the air relief valve on top of the filter. This lets trapped air escape instead of fighting the pump.
- Remove the pump lid and empty the strainer basket. A basket packed with leaves is a common reason a pump “will not prime”.
- Fill the pump housing with the hose until water stops draining away into the suction pipe and sits at the top of the housing. On some pools this takes a full minute or two of running the hose because you are filling the suction line too.
- Inspect the lid o-ring. Wipe it clean, look for cracks or flat spots, add a thin film of lubricant, and seat it in its groove. Replace the lid hand-tight. A tiny gap here is the number one cause of lost prime.
- Turn the power on and watch the basket. You will see churning, then bubbles, then a full, clear basket as water arrives from the pool.
- Close the air relief valve once a steady stream of water (not sputtering air) comes out of it.
- Check the return jets. Strong flow with no bubbles means you are primed. A variable-speed pump should be primed at high speed; most have a priming mode that runs fast for the first few minutes on their own.
If the basket has not filled within about five minutes, turn the pump off, top up the housing again, and go to the troubleshooting list below. Do not let it keep running dry.
Priming an above-ground pool pump
Most above-ground pumps sit below the water line, so gravity does the work. Open the valves (or remove the plugs) on the skimmer and return hoses, crack the air release on top of the filter or pump until water comes out, close it, then switch on. If an above-ground pump will not prime, look for a kinked or collapsed suction hose, a hose clamp letting in air, or a water level below the skimmer. More on these pumps in our above-ground pool pump guide.
Pool pump won’t prime? Work through these in order
1. The water level is too low
The cheapest fix and the most common. If the skimmer is sucking air (you will hear it gurgle and see a vortex), add water until it is halfway up the opening.
2. Something is clogged
Check the skimmer basket, the pump basket and, if both are clear, the impeller. A pine needle cluster or a small toy stuck in the impeller eye chokes flow. With the power off, reach through the basket opening and feel for debris.
3. Air is leaking in on the suction side
Anything between the pool and the impeller that lets air in will break prime. The usual suspects, cheapest first: the pump lid o-ring, a loose or missing drain plug o-ring on the pump housing, a cracked threaded fitting going into the pump, a leaking valve stem, and the shaft seal. The giveaway is a steady stream of bubbles in the pump basket, or bubbles blowing out of the return jets, while the pump runs.
Quick test: with the pump running, smear a little shaving cream around each suspect fitting on the suction side. Where the cream gets sucked in, you have found the leak.
4. A valve is closed or half-closed
After a cleaning or winterizing, a skimmer or drain valve often gets left shut. Also check that the multiport valve is fully seated on “Filter” and not between positions.
5. The pump is too far above the water
Self-priming pumps can only lift water so far. If the equipment pad sits several feet above the pool, priming takes longer, and a check valve on the suction line is worth installing so the line stays full between runs.
6. The pump itself is worn
A worn impeller, a failed shaft seal (often with a drip under the motor) or a cracked housing will keep a pump from priming no matter what you do outside it. At this point you are deciding between a repair and a replacement. Our pool pump repair page covers what each fix usually costs, and you can request a quote from a local pro there.
Parts that fix most priming problems
A new lid o-ring and a set of drain plug o-rings cost less than a pizza and solve a large share of priming complaints. Match the part to your pump brand and model (it is printed on the motor label).
Shop pool pump lid o-rings on Amazon
Brand-specific help: Hayward pool pumps and Pentair pool pumps.
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FAQ
How long should it take a pool pump to prime?
Usually 1 to 3 minutes. Pumps that sit well above the water line or have long suction runs can take up to 5. Past that, stop and troubleshoot.
Can I run a pool pump without priming it?
No. The shaft seal is cooled and lubricated by water. Running dry can overheat and crack it within minutes, which then leaks and lets in more air.
Why does my pool pump lose prime overnight?
Water is draining back to the pool through a small suction-side leak or a valve that does not hold. Replace the lid and drain plug o-rings first; if it continues, a check valve on the suction line usually stops it.
Do variable-speed pumps need to be primed?
Yes, the same way. Most run a built-in priming cycle at high speed for the first few minutes. If you lowered that setting, prime manually at a higher speed, then drop to your normal run speed.
Should I prime with the filter valve on backwash?
No. Leave it on “Filter”. Backwash sends the water you are trying to circulate out the waste line.
The 60-second call
Power off, check the water level, clean the basket, fill the housing, lube and seat the o-ring, power on, bleed the air. If it will not catch in five minutes, look for air leaks on the suction side before you blame the pump. And if the pump is the problem, get a repair quote or use the pool pump calculator to size a replacement and see what a variable-speed model would save.