A pool pump only does one thing: pull water from the skimmer and main drain and push it through the filter, heater and back to the returns. It cannot pull air, so any air that sneaks in on the suction side (everything between the pool and the pump) shows up as a pump that will not catch prime, loses prime overnight, or churns bubbles in the lid. That is where to start, and it is where most of the fixes are.
First, the suction side
Water level. Mid-skimmer. Below the skimmer mouth the weir door gulps air every time a wave passes and the pump loses prime; a pool that dropped after a hot windy week is the classic cause.
Both baskets. The skimmer basket and the pump basket, emptied and seated properly. A pump basket that is cracked, missing or sitting crooked lets debris into the impeller and air around the seal of the lid.
The lid and its o-ring. The pump lid o-ring is the single most common air leak on a pool pad. Pull it, wipe the groove, look for flat spots and cracks, lubricate it with a silicone pool lube (never petroleum), and seat the lid hand-tight. A dry, cracked or stretched o-ring is a parts-counter fix.
Valves, plugs and unions. Every suction valve open, the drain plugs back in the pump and the filter (they were pulled at closing and stored in the pump basket; after an opening they are the first thing to check), unions snug, the valve stems not weeping. A valve stem o-ring that lets air in at speed is invisible until you look for bubbles in the lid.
The weir door and the skimmer. A weir door stuck up starves the skimmer; one stuck down lets the basket float. A cracked skimmer throat is a water leak when the pump is off and an air leak when it is on, which is why some pumps only misbehave at full speed.
How to prime it properly
- Pump off. Fill the pump pot to the top with a hose and put the lid on with the clean, lubricated o-ring.
- Open the air relief on top of the filter. Open the skimmer valve; if the pump struggles, close the main drain valve for the first attempt so it lifts from the skimmer only.
- Start the pump and give it a full two or three minutes. Water sputters, then runs clear in the lid; close the air relief when water sprays from it instead of air.
- No catch after three minutes: stop, refill the pot and try again. A pump that will not catch after two or three honest tries has a real air leak or a blockage, and running it dry cooks the shaft seal.
- Variable-speed pump: prime at high speed, then let the schedule drop it. A low speed set too low will not pull prime at all, and some pads need a higher minimum speed than the factory default.
Then, what the pump is telling you
| What you see | What it usually means | Your move |
|---|---|---|
| Will not prime at all | Air leak on the suction side, water below the skimmer, a clogged impeller, a closed valve, or a drain plug still out. | Water level, baskets, lid o-ring, valves and plugs; prime from the skimmer only. Still nothing: the impeller or a suction line. |
| Primes, then loses prime overnight | A small suction leak (lid o-ring, union, valve stem), low water, a stuck weir door, or a cracked pump pot. | Watch the lid for bubbles at speed. No bubbles and still losing prime: the pot or a suction line, which is a visit. |
| Bubbles in the lid or from the returns | Air entering on the suction side, or low water at the skimmer. | Same list, in order: level, baskets, lid o-ring, unions, valve stems. |
| Screaming, grinding, growling | Motor bearings. The wet end is usually fine; the motor is dying. | Call before it seizes. Motor replacement, or a variable-speed pump if the old one is tired anyway. |
| Hums, will not start | A failed start capacitor, or a seized shaft from debris or a dry seal. | Power off. If the shaft will not turn by hand, it is a technician's job; a capacitor is a quick one. |
| Trips the breaker | Wet motor, seized bearings, or wrong voltage after a replacement. | Leave it off and call. |
| Drips at the back of the wet end | Shaft seal. Running dry, even briefly, is the usual cause. | A seal and gasket job; done soon, the motor survives. Ignored, water reaches the bearings. |
| Weak returns, low flow | Dirty filter, a clogged impeller, half-closed valves, a leaf trap full at the skimmer, or an undersized or worn pump. | Clean the filter first; most low-flow calls are the filter, not the pump. |
| Filter pressure very high, pump fine | The filter, not the pump. | Backwash or clean the cartridge; a sand change if it has been a couple of seasons. |
Pool leak or pump leak?
Water dripping from the pump is a pump problem; a pool level that drops with the pump off is a pool problem; air in the pump with the level steady is a suction leak somewhere between the skimmer and the pad. They get confused all the time. The bucket test on our pool leak detection page separates the first two in a day.
When to stop and call
Grinding or screaming, a breaker that trips, water coming out of the motor, a cracked pump pot after a freeze, or a pump that will not hold prime after the suction list is clean. The service department repairs and replaces pumps and motors across the Omaha metro, on the pools we built and the ones we did not, with Hayward, Pentair, Waterway and Polaris parts on the shelf at Wright Plaza; what to have ready is on the pool repair page. A pump that is tired anyway is the moment to talk about a variable-speed pump, which primes gently, runs quieter and costs far less to run.
How to not read this page again
- Baskets weekly, both of them. Skimmer baskets and lids are at the store if one is cracked.
- Lid o-ring lubed every opening and replaced when it flattens. Pump and filter parts on the shelf.
- Water at mid-skimmer. Especially after a hot, windy week.
- Drain it every fall. Plugs out, stored in the basket; our closing crew does exactly that, and the opening puts them back and primes the system.
- Or put the pad on a plan. Baskets, pressure and a look at the pump every visit: pool service plans.
Heater or hot tub instead? Same first rule, different page: pool heater won't ignite · hot tub won't heat / error codes.
Frequently asked questions
Why won't my pool pump prime?
Air is getting in on the suction side or there is not enough water to pull. Check the water level (mid-skimmer), empty and seat both baskets, clean and lubricate the pump lid o-ring, open every suction valve and make sure the drain plugs are back in, then fill the pump pot and prime from the skimmer only. If it still will not catch after a few honest tries, the impeller or a suction line needs a technician.
Why does my pool pump lose prime overnight?
A small air leak the pump can overcome while running but not while it sits: a lid o-ring, a union, a valve stem, or a cracked pump pot. Low water and a stuck weir door do it too. Watch the lid for bubbles while it runs; no bubbles and still losing prime usually means the pot or a buried suction line.
Why is my pool pump so loud?
A high-pitched scream or a grinding growl is the motor bearings. The wet end is usually fine; the motor is wearing out. Have it looked at before it seizes, and if the pump is old, a variable-speed replacement is quieter and cheaper to run.
My pool pump hums but won't start. What is wrong?
Usually the start capacitor, or a shaft seized by debris or a seal that ran dry. Power off at the breaker; if the shaft will not turn by hand, it is a repair visit. A capacitor is a quick one.
Is it the pump or the filter?
Look at the filter gauge. Pressure much higher than the clean reading with weak returns is a dirty filter, not a pump. Low pressure with weak returns and air in the lid is the pump side. Clean the filter first either way.
Do you repair pool pumps you didn't install?
Yes. Pumps and motors on inground and above-ground pools across the Omaha metro, whoever built the pool, with Hayward, Pentair, Waterway and Polaris parts on the shelf at the store. Details and what to have ready are on the pool repair page.