Guide
Centrifugal Pump Troubleshooting Guide
A comprehensive troubleshooting guide for centrifugal pumps — covering no flow, low flow, low pressure, vibration, overheating, and leaks. Quick-reference tables to diagnose and fix any pump problem.
11 min readUpdated July 2026
Symptom: No Flow
- Pump not primed — vent the casing and fill with liquid
- Suction valve closed — verify all valves in the suction line are open
- Suction strainer blocked — clean the strainer
- Discharge valve closed — verify discharge path is open
- Pump running backwards (three-phase motor) — swap two phases and verify rotation
- Air leak in suction line — check all fittings and gaskets
- Impeller blocked or damaged — inspect and clean or replace
- Suction lift too high — verify NPSHa exceeds NPSHr
- Foot valve stuck closed — inspect and clean
Symptom: Low Flow
| Possible Cause | How to Check |
|---|---|
| System resistance higher than expected | Compare actual discharge pressure to pump curve at expected flow |
| Worn impeller or wear rings | Measure internal clearances, compare to OEM specs |
| Cavitation | Listen for gravel sound, check NPSHa |
| Air entrainment | Check for air bubbles in sight glass, inspect suction fittings |
| Impeller partially blocked | Inspect impeller through casing |
| Suction strainer partially blocked | Check differential pressure across strainer |
| Pump speed too low | Verify motor speed and frequency (VSD) |
| Wrong rotation direction | Check rotation arrow on casing |
| Worn mechanical seal leaking air | Inspect seal area for leaks |
Symptom: Low Pressure
- Impeller worn — reduced diameter means reduced head. Replace or trim to correct size.
- Wear rings worn — internal recirculation reduces discharge pressure. Replace.
- Cavitation — vapour bubbles reduce the effective head. Check NPSH.
- Air entrainment — reduces pump density and causes unstable pressure.
- Speed too low — verify motor speed, check VSD settings.
- Wrong impeller size — verify impeller diameter matches the curve.
- System demand higher than pump capacity — pump is running out to the right of curve.
- Worn casing volute — internal erosion reduces efficiency.
Symptom: Vibration
| Vibration Type | Likely Cause |
|---|---|
| 1× running speed, radial | Unbalance, eccentric rotor |
| 2× running speed, axial | Misalignment |
| Multiple harmonics | Mechanical looseness, soft foot |
| High frequency (5–20 kHz), broadband | Cavitation |
| Vane pass frequency | Impeller vane passing the volute tongue |
| Sub-synchronous | Oil whirl, belt resonance |
| Bearing tones (BPFI/BPFO/BSF) | Bearing defect — use envelope analysis |
Symptom: Pump Overheating
- Operating at or near shutoff (low flow) — install minimum flow bypass
- Cavitation — check NPSH, clean strainers
- Bearing failure — check temperature and vibration
- Over-greasing — reduce grease quantity
- Misalignment — laser-align the coupling
- Insufficient cooling water — verify flow to bearing housing jacket
- High ambient temperature — improve ventilation
- Seal running dry — verify seal flush is operational
Symptom: Leaks
| Leak Location | Cause | Fix |
|---|---|---|
| Mechanical seal | Dry running, worn faces, chemical attack | Replace seal, fix root cause |
| Gasket joints | Loose bolts, damaged gasket | Replace gasket, re-torque bolts |
| Casing | Corrosion, erosion, or cracking | Repair or replace casing |
| Packing gland | Worn packing, wrong packing size | Replace packing, adjust gland |
| Valve stem | Worn packing, damaged stem | Repack or replace valve |
Symptom: Motor Trips
- Operating too far right on the curve (excessive flow) — throttle discharge or trim impeller
- Liquid density higher than design — verify SG and resize motor if needed
- Mechanical friction (bearings, seals) — check for free rotation
- Low voltage — check all three phases
- Voltage imbalance — verify all phases within 2%
- Motor winding degradation — megger test
- Starting against full system pressure — start with discharge cracked open
- Overload relay set too low — verify setting matches motor FLA
Pro tip: Always start troubleshooting with the simplest checks first — valve positions, strainer condition, rotation direction, and prime. These account for over 50% of pump problems and take minutes to verify. Only move to more complex diagnostics (vibration analysis, pump curve analysis) after the basics are confirmed.