The pump divides the system. Suction side is before the pump; pressure side is after. Symptoms point you toward one side -- but symptoms are clues, not confirmation. Testing confirms it.
Learn the H.U.N.T.E.R. Method →Air in the pump basket, pump losing prime, and bubbles returning through the returns typically suggest the suction side. Water loss that gets worse when the pump runs typically suggests the pressure side. These are clues -- not proof. The equipment pad, valve isolation, pressure testing, and dye testing are what confirm which side and which component is actually leaking. Many pool leaks are not in the plumbing at all, and no pump behavior fully rules out shell, fitting, light, or drain-area sources.
The pump is the dividing point. Everything between the pool openings and the pump inlet is the suction side. Everything between the pump outlet and the pool is the pressure side.
| Symptom | Suggests | Caution |
|---|---|---|
| Air in pump basket | Suction side | Equipment pad leaks, pump lid O-ring, or drain plug can also cause this |
| Pump loses prime | Suction side | Confirm it is the suction circuit, not a pump lid or seal issue |
| Bubbles return from return fittings | Suction-side air entering the system | Small amounts may come from equipment, not a plumbing break |
| Water loss increases when pump runs | Pressure side | May also indicate a waterfall or spa that only runs with the pump on |
| Wet equipment pad | Equipment pad leak -- either side | Inspect the pad directly before assuming underground plumbing |
| Loss only when cleaner booster runs | Booster cleaner circuit (pressure side) | Isolate and test the booster circuit specifically |
| Loss only with spa jets on | Spa plumbing or spillover | May be valve bypass, not an underground leak |
| Loss only with waterfall on | Waterfall circuit | May be splash, wind drift, waterproofing -- not a pipe break |
| Loss with pump completely off | Shell, fitting face, drain, or static fitting | Neither suction nor pressure plumbing is the cause -- look at the vessel |
Pump-on/pump-off behavior and air symptoms are directional clues -- they narrow the inspection but do not finish the diagnosis. Equipment pad leaks, valve stem leaks, pump lid O-ring failures, and backwash line losses can all create suction or pressure-side symptoms without any underground pipe break being involved. Always inspect the pad before chasing underground plumbing.
Before assuming underground plumbing, inspect the equipment pad. A surprising number of "suction-side" and "pressure-side" symptoms originate here:
Use valve isolation to narrow which circuit is involved:
When symptoms change as valves change, the technician has narrowed the circuit involved.
Once a circuit is narrowed, pressure test the isolated line. A pressure drop (after setup verification) confirms the line is losing pressure. It does not locate the break or rule out adjacent leak sources.
Dye testing confirms local active water movement -- at return fitting faces, skimmer throats, light conduits, hydrostatic valves, cracks, and gaskets. Use dye after pressure testing to cover what the pipe test cannot answer.
Some leaks only appear under specific conditions. Verify under the exact mode -- spa on, waterfall running, booster running, or pump off -- that the customer reported the loss. A test under the wrong operating condition is not a complete test.
Ask when the loss happens, what equipment is running, whether there is air in the pump, and whether the pattern changes with different valve positions or operating modes.
Map the full system -- suction side, pressure side, equipment pad, spa, cleaners, and water features. Know every component before drawing a conclusion.
Use pump behavior, valve isolation, and operating mode to narrow which side and which circuit is involved. Inspect the equipment pad before chasing underground plumbing.
Pressure test the isolated circuit. Dye test fitting faces and shell points. Test under the actual operating mode that produces the reported loss.
Confirm the actual source -- not just the likely side. Equipment pad leaks, valve bypass, and shell leaks can all produce symptoms that look like plumbing failures.
Repair the confirmed source. Verify under the same operating conditions that produced the original loss. Document the full diagnostic path.
Sees air in the pump basket and assumes an underground suction line is broken. Skips the equipment pad inspection. Ignores the pump lid O-ring. Pressure tests the skimmer line, it passes, still has no explanation for the air.
Checks the pump lid O-ring, pump drain plugs, and pad valves first -- because most residential suction-side air starts there. Uses valve isolation to narrow the circuit. Confirms with pressure testing and dye testing. Treats symptoms as clues, not conclusions.
Jeff David is the founder of Leak Business Academy, LLC and Leak and Subsurface Locators, LLC. He is a licensed pool contractor in Florida and an FSPA Palm Beach board member. Jeff teaches the H.U.N.T.E.R. Method -- including why suction/pressure classification is a starting point for the inspection, not a conclusion, and why the equipment pad must be inspected before any underground plumbing is tested or blamed.
LBA training covers pump behavior analysis, valve isolation technique, equipment pad inspection, pressure testing, dye testing, and operating-mode testing -- so technicians find the actual source every time.
View Training Resources Get the Pool Leak Detection Guide