Is my Pool Skimmer Clogged or is it a Plumbing Issue?

Alex Kelly • August 10, 2025

Homeowners guide to determining if your Pool Suction Lines are clogged or broken.

When your pool stops circulating right, besides a clogged filter, or a stuck backwash valve, it almost always comes down to two culprits on the suction side: a clog or a broken suction line. The fastest way to tell the difference is to watch your pump basket, and pressure gauge and by listening to your pump. A clogged filter is always a possibility but will be obvious by a high pressure gauge! Below is a clear, step‑by‑step way to diagnose what you’re dealing with—using your own senses and perception, without guesswork, or risking damage.

Symptom Snapshot
Symptom Clogged Line Broken/Air-Leaking Line
Pump prime Holds prime but water reduces Loses prime or surges
Pump basket level Low and steady Foamy, surging, erratic
Return jet flow Weak or nonexistant Pulsing, spitting air
Sound Steady strain motor load Motor surging from cavitation
After shutdown Basket refills instantly Water expelled, restart struggles
Filter pressure None/Low/Reduced from Normal Erratic; may swing with surges

Clogged line (leaves, toys, skimmer sock, etc.)

  •  The pump stays primed but moves very little water.
  •  The water level in the pump basket slowly draws down and sits low and “lazy,” with minimal turbulence.
  • Flow at returns is weak but consistent (no violent surging).
  • When you shut the pump off, the pump basket fills back up immediately—because the system didn’t actually move much water through due to the clog.
  • Sound: steady hum working “hard,” not gurgling.

Broken/air‑leaking suction line (skimmer line, main drain, vac-line, or valves and fittings)

  • Despite repeatedly filling the pump with water to begin, air is consistently drawn into the system; the pump repeatedly loses prime or “surges.” 
  • You’ll see a stream of bubbles enter under the clear pump lid; water level drops rapidly and rises erratically as suction builds, but then another pocket of air enters.
  • Return jets spit air; you may see bubbles at the spa spillway or returns.
  • Depending on the severity of the air leak, restart is stubborn until air is purged, smaller cracks and breaks can cause mini cavitations and an erratic pump operation, it can also manifest as an increased amount of air in the pump basket, yet stil operating near prime.
  • Sound: Cyclical hollow, rattly, or “gravelly” cavitation as the impeller catches air, followed by the increasing hum the pump motor makes while attempting to reach prime again before more cavitation occurs repeating the sound of the full cavitation.

The core difference in behavior (clog vs. broken suction line)

How your suction side works (quick refresher)


  • Skimmer(s), Main drains, and suction side vacuum cleaner lines feed the pump on the suction side. Any restriction (clog) reduces flow; any breach lets air in.


  • The pump must stay fully flooded to avoid cavitation. Air in the line breaks the continuous water column and the pump chews pockets of air instead of water—your classic surge/lose‑prime behavior.


Do this diagnosis at the equipment pad

  1. Isolate lines one at a time
  2. Set valves to run on main drain only. Note behavior.
  3. Set valves to run on skimmer only. Note behavior.
  4. If it surges only on one setting, the issue is on that line.
  5. Watch the pump basket
  6. Low, steady water level = restriction (clog).
  7. Foam, constant bubbles, rising/falling level = air leak/broken line.
  8. Check easy false positives first
  9. Skimmer basket cracked or overfull; stuck weir door; skimmer sock packed with debris.
  10. Pump lid O‑ring dry/dirty; unions hand‑tight; Jandy style 3‑way valve stems leaking. or outer o-ring damage.
  11. Filter extremely dirty (backwash/clean to rule out pressure‑side restriction).
  12. The shutdown test (fast tell)
  13. If you shut the pump off and the basket instantly floods full, you likely have a clog (not cavitation).
  14. If you shut down and see the water level stay the same as the pump has pushed all the water out, suspect an air leak/breach.
  15. The hose “blow‑back” test (for clogs)
  16. With power off and valves isolating the suspect line, remove the pump basket and push a garden hose into the suction port. Seal loosely with a rag and run water to back‑flush debris toward the skimmer. Catch debris at the skimmer.
  17. Do not over‑pressurize; if resistance is extreme, stop and call a pro.
  18. With the pump running, brush a mild soapy solution around suction side unions, lid, and valve stems. If soap gets pulled in and you see momentary bubble changes under the lid, you’ve found a suction‑side air leak.


Broken pool skimmer being demolished for replacement.

Common causes


Clogs

  • • Vacuuming without a Leaf canister filter on your hose.
  • • Not replacing damaged Main Drain Covers, or not properly attaching covers
  • • Skimmer sock overloaded, or broken or damaged skimmer baskets allowing excess fine debris to clog impeller/diffuser or pump basket.
  • • Toys, pinecones, heavy leaf fall, acorns, fine plant debris that sinks; like spring tree flowers and other fine seeds
  • • Impeller partially blocked (behind the pump basket)


Air leaks/broken suction

  • • Hairline crack in skimmer throat or line (often after freeze/thaw)
  • • Settled deck stressing fittings
  • • Loose pump lid, worn O‑ring, dry unions
  • • Valve stem seals leaking
  • • Underground pipe fracture pulling air when pump runs

What not to do


  • Don’t run the pump for long periods of time while it’s cavitating—this overheats seals and can warp or even totally melt the pump basket/cover, and up pipe from the pump to the filter, and cause swelling and a need for replacement.
  • Don’t pour acids or harsh chemicals into the skimmer to “clear” a clog—this can damage equipment and plumbing.
  • Don’t hammer the hose with high pressure or compressed air without isolation and relief; you can burst fittings.


Quick fixes you can try safely


  • Empty/replace damaged skimmer basket; free the weir door.
  • Remove skimmer sock; clean or replace.
  • Lubricate and reseat the pump lid O‑ring; hand‑tighten unions.
  • Backwash/clean the filter to remove downstream restriction.
  • Perform a gentle hose back‑flush of the suspect suction line.
  • If the impeller is blocked: with power off, remove the pump basket and feel for debris at the impeller eye; clear carefully.


When to call a pro


If the pump surges, or won’t hold prime on a specific suction line, or you suspect an underground breach, it’s time for professional pressure testing and acoustic pinpointing. That’s where precise diagnostics save you from unnecessary digging and guesswork. We can isolate each line, pressure test it, and, if needed, locate and repair underground breaks cleanly with minimal deck impact.

  • Prefer a lasting fix over a “patch and pray” approach? That’s our lane.
  • Need fast turnaround during swim season? We schedule diagnosis and repairs efficiently to keep your pool usable. Pool downtime measured in days not weeks for repairs.


FAQs

  • Why does my pump basket level sit low but steady?
  • That’s a classic restriction profile. The pump is moving less water, not gulping air. When you stop the pump, the pot fills instantly because the water column remained intact.
  • Why does my system surge and spit bubbles?
  • Air is entering the suction side. The impeller cavitates, breaking prime. Look for lid/unions/valves above ground first; if those check out, the line itself may be compromised.
  • Can a dirty filter mimic a clog?
  • A heavily loaded filter restricts the pressure side and can lower overall flow, but it won’t usually cause suction‑side air under the lid. Clean/backwash to remove that variable.


Need help now?


Describe your symptoms (surging vs steady low flow, which valve positions, what you see under the lid), and we’ll tell you your next best step—or get you on the schedule for a service call or leak detection and a repair that lasts.

Contact us


Need help diagnosing a leak? See our pool leak detection services.


Wondering if it’s evaporation or a leak? Try our pool evaporation calculator.

The Leak Report

Real estate inspection for in-ground swimming pools.

Why Realtors Should Always Get a Pool Inspection

By Alex Kelly • July 27, 2025
Why using a Leak Detection Company for your Pool Inspection is a Must.
A completed plumbing repair on a pool, under the pool's concrete deck.

Why should you choose Manly Maids for your Pool Leak Detection, and Leak Repairs

By Alex Kelly • July 15, 2025
This image shows a competed pool plumbing repair, a broken PVC pipe has been re-plumbed under the pool deck. Now it will be re-filled, compacted and concrete poured.
Performing a bucket test

Bucket Test: An in-depth guide to test if your pool is leaking

By Alex Kelly • July 26, 2024
What is the Bucket Test for Pool Leak Detection? Have you ever noticed your pool’s water level mysteriously dropping? Often, it’s not due to evaporation alone; your pool might be signaling that it has a leak.

Book a Service Today