Domakihub Pool Pump Keeps Losing Prime: Fix Suction-Side Air Leaks
A step-by-step guide to finding and sealing every suction-side air ingestion point before the pump fails entirely.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
If your pool pump re-primes after you fill the pot, runs for a while, then loses suction again, you have a suction-side air leak — not a pump fault. The video above walks through the most common leak points visually; this article gives you a systematic checklist you can follow on any Greek property, whether it is a private villa, a holiday rental, or a hotel pool. Catching the leak early saves the pump motor from running dry and avoids an emergency call-out mid-season.
Why Air on the Suction Side Is So Destructive
A pool pump is designed to move water, not air. When air enters anywhere between the skimmer and the pump inlet, the impeller loses its grip on the water column, flow drops, and the pump cavitates — producing that characteristic rattling or gurgling sound. Left unchecked, cavitation erodes the impeller, overheats the seal, and eventually seizes the motor.
In Greece the problem is amplified by summer heat. UV degradation softens O-rings and shrinks PVC unions faster than in cooler climates, and underground pipe joints that have been dormant since last winter often open slightly as soil temperature rises. A leak that was invisible in April can starve a pump completely by July.
The Golden Rule: Isolate Before You Seal
Never apply silicone or thread tape to a fitting you have not confirmed is leaking. Chasing a ghost leak wastes product and can mask the real source. The correct approach is to work from the pump backward toward the pool, testing one section at a time, so you know exactly which component is at fault before you take anything apart.
How to Find and Fix Suction-Side Air Leaks
- 1
Inspect the strainer lid and O-ring first
Remove the clear strainer lid and examine the O-ring. It should be pliable, uniformly round, and free of cracks or flat spots. A dried-out or pinched O-ring is the single most common air ingestion point. Clean the groove with a damp cloth, coat a new O-ring lightly with a silicone-based lubricant (never petroleum jelly), and reseat it carefully before screwing the lid down hand-tight. Do not overtighten — that deforms the O-ring and creates a new leak.
- 2
Check every union fitting on the suction line
Union fittings allow the pump to be removed for servicing, and their threaded collars work loose over time through vibration and thermal cycling. With the pump running, hold a sheet of tissue paper near each union: if it gets pulled toward the fitting, air is entering there. Turn the pump off, unscrew the union, inspect the internal O-ring or gasket, replace it if it shows any deformation, re-lubricate, and retighten. Check both the suction-side and the union immediately before the pump body.
- 3
Test valve stems and valve bodies
Multiport valves and gate valves on the suction line have stem seals that degrade just like any other O-ring. A slow leak around a valve stem is easy to overlook because it may only admit air when the pump is under high negative pressure. With the pump running, apply a thin line of shaving foam or diluted washing-up liquid around each valve stem and along valve body seams — any foam that gets drawn inward or produces moving bubbles marks the leak. Replace the stem O-ring or valve cap seal as directed by the valve manufacturer.
- 4
Examine above-ground pipe joints and glued couplings
Solvent-welded PVC joints that were assembled in cold weather or with insufficient primer sometimes develop micro-gaps that only open under suction. Run the shaving-foam test along every joint you can see. If a joint is confirmed leaking, cut it out cleanly with a pipe cutter, dry-fit a replacement coupling with fresh primer and PVC cement, allow the full cure time stated on the cement tin before refilling (typically two hours minimum in warm weather), and retest.
- 5
Pressure-test underground sections if the above steps find nothing
If all visible components test clean but the pump still loses prime, the leak is underground. Plug the skimmer throat and the pump inlet temporarily, attach a pressure gauge to a drain plug port, and pressurise the suction line to around 10 psi with a hand pump. A steady pressure drop over five minutes confirms a subsurface pipe fault. At this point the repair requires locating the break — sometimes via acoustic leak detection — and either excavating to patch the joint or inserting an epoxy pipe-liner. This is the stage at which calling a qualified pool technician is the right decision; they carry the specialist equipment to find the fault without unnecessary digging.
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FAQ
- Can I use Vaseline to lubricate the strainer lid O-ring?
- No. Petroleum-based products like Vaseline attack rubber over time, causing the O-ring to swell and then crack. Always use a dedicated silicone lubricant or a food-grade silicone grease, both of which are widely available at pool supply shops across Greece.
- How do I know the air leak is on the suction side and not the pressure side?
- Suction-side leaks pull air in, so you will see persistent bubbles returning through the return jets into the pool, and the water level in the strainer pot will drop when the pump is off. Pressure-side leaks push water out, so you would see a wet patch or drip near the filter or return plumbing. If your pot runs dry and the return jets are airy, the fault is upstream of the pump.
- My pump loses prime only at night. Why does it happen at a specific time?
- Temperature swings between the hot Greek afternoon and cooler evenings cause PVC pipes and fittings to contract slightly. A fitting or union that seals adequately when warm may open just enough at night to admit air. This points to a marginal O-ring or a union that needs one more quarter-turn of tightening — check every union and the strainer lid seal first, then move on to valve stems if tightening does not resolve it.