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Pump Fault – Initial Troubleshooting (VFD / motor)

This guide describes a systematic, field-proven approach for troubleshooting pump, motor, and drive-related faults on LiqTech filtration systems. It applies to centrifugal pumps driven by VFDs and protected by motor protection devices.

When to use this guide

Use this guide when:

  • A pump fault alarm is active on the HMI

  • The pump does not start when commanded

  • The pump trips during ramp-up or shortly after start

  • The VFD shows a local fault

  • A motor protection device or breaker has tripped

Preconditions and safety

  • The system should normally be in STOP state

  • Live testing may be required to observe pump behavior during start

  • Troubleshooting shall only be carried out by competent personnel with:

    • Electrical knowledge

    • Process understanding

    • Familiarity with rotating equipment

  • Always ensure:

    • The pump is not running dry

    • The pump is not running against a closed valve

    • Strainers are not blocked

  • Follow site-specific lock-out / tag-out procedures when required

Typical symptoms

  • Pump does not start

  • Pump starts briefly and trips

  • Repeated trips after reset

  • VFD shows a local fault

  • HMI shows pump fault or network communication alarm

  • Pump runs but delivers no flow

Step-by-step troubleshooting procedure

1. Check the obvious first (very important)

Before deeper troubleshooting, always verify:

  • Has anything tripped in the electrical cabinet?

    • Motor protection device

    • Circuit breaker

  • Is the pump drive powered?

  • Does the VFD display show a local fault or alarm?

  • Has the fault been:

    • Reset locally on the VFD

    • Reset on the HMI

👉 A large share of reported pump problems are resolved at this stage.

2. Can the pump rotate freely? (early and critical check)

Before electrical measurements or parameter checks:

  • Verify the pump shaft can rotate freely by hand

  • Check for:

    • Mechanical blockage

    • Seized bearings

    • Foreign objects in the pump

👉 If the pump cannot rotate freely, do not proceed with electrical troubleshooting.

3. Distinguish local VFD fault vs. network communication alarm (critical)

Local VFD fault (must be cleared first)

  • A fault is visible on the VFD display

  • The VFD is not operational

  • The pump will not run until the fault is cleared locally

Action:

  • Clear all local VFD faults

  • Ensure the VFD is:

    • Powered

    • Fault-free

    • Ready for operation

👉 A VFD must be fault-free before network communication can be expected to work.

Network communication alarm (HMI)

  • The VFD may be electrically healthy

  • Communication between PLC and VFD is lost

  • Common on daisy-chained VFD networks

  • A powered-down or faulted drive can block communication for others

Action:

  • First verify the VFD is powered and fault-free

  • Check that Ethernet connectors are correctly seated

  • Verify the IP address matches the electrical documentation

  • Inspect network cables and connectors for damage

  • Only after this, proceed with further network diagnostics

👉 A network alarm does not necessarily indicate a pump or motor fault.

4. Observe how the fault occurs

If the fault persists, observe:

  • Does the pump:

    • Not start at all?

    • Start and trip immediately?

    • Trip during ramp-up?

  • Does the fault appear:

    • Only on start command?

    • After a few seconds?

    • Together with other pump or network alarms?

👉 Fault timing is often the fastest diagnostic clue.

5. Mechanical and process checks

Confirm that the pump is not being forced to operate under unfavorable conditions:

  • Ensure the pump is:

    • Properly primed

    • Not running dry

    • Not running against a closed discharge valve

  • Check:

    • Suction strainer condition

    • Blockages upstream or downstream

6. Controlled low-speed test from HMI (recommended)

The pump can be operated at low speed directly from the HMI.

Procedure:

  • Select the pump on the HMI

  • Enter a low speed setpoint (e.g. 5%)

  • Start the pump briefly

Use this test to:

  • Verify the pump is able to run

  • Confirm correct rotation direction

  • Observe abnormal noise or vibration

Correct rotation direction:

  • The pump shall rotate clockwise

⚠️ Only perform this test when it is confirmed that the pump is not running dry and not operating against a closed valve.

7. Electrical supply and motor checks

If mechanical and process conditions are acceptable:

  • Verify all phases are present

  • Check for:

    • Phase loss

    • Phase imbalance

  • Confirm sufficient power supply:

    • Especially important with DG (diesel generator) supply

    • Ensure generator capacity and voltage stability

  • Inspect motor cables and terminals for overheating or damage

⚠️ Electrical checks shall only be performed by qualified personnel.

8. VFD parameter and protection checks

If the VFD shows a local fault:

  • Read and note the exact fault code

  • Verify:

    • Motor rated current

    • Voltage

    • Frequency

    • Acceleration / ramp-up time

  • Check for:

    • Overcurrent

    • Torque limit

    • Stall or overload faults

👉 Ramp-up settings should only be adjusted after mechanical and process conditions have been verified.

9. Reset and verify

After corrective actions:

  • Reset:

    • Motor protection device

    • Local VFD fault

    • HMI alarm

  • Allow the system to stabilize for a few minutes

  • Start the pump and observe:

    • Ramp-up behavior

    • Current draw

    • Flow response

Field insight – most common root causes

In practice, pump faults are most often caused by:

  • Mechanical blockage or seized pump

  • Incorrect rotation direction

  • Dry running

  • Closed discharge valve

  • Blocked strainer

  • Phase loss or unstable power supply

  • Insufficient generator capacity

Actual motor or VFD hardware failure is less common.

Field insight – multiple pumps affected

If multiple pumps show faults or communication alarms at the same time:

  • Check common power supply

  • Check generator load and stability

  • Check the VFD communication chain

👉 Multiple pump issues usually indicate a system-level problem.

When to stop and contact LiqTech Service

  • If pump trips persist after mechanical, process, and supply checks

  • If VFD fault codes indicate internal drive failure

  • If network communication faults cannot be cleared

  • If pump operation poses a safety risk

    Alarm ID references – Pump Fault / Pump Trip / Pump Not Running (examples)

    The following alarm IDs are non-exhaustive examples of pump-related alarms observed across different LiqTech Crossflow systems.
    They are provided to help support agents recognize the alarm type when a customer references a specific alarm number.

    Other alarm IDs with similar alarm texts may exist depending on system generation and project configuration.

    MK6 – Numeric alarm IDs

    Pump motor / protection / overload
    21
    22
    23
    24
    25

    Pump not running / no feedback
    68
    69
    70
    71
    72

    Pump trip during operation
    118
    119
    120
    121
    122

    Pump / drive fault (general)
    178
    179
    180
    181

    MK6 alarms typically repeat per pump and per module.

    MK8 / project-based systems – D-series

    Pump fault / motor protection
    D0004
    D0101
    D0102
    D0201
    D0303
    D0304
    D0417
    D0418
    D0419
    D0601

    Pump not starting / pump stopped
    D0203
    D0204
    D0501
    D0502

    MK8 / FM01 – F-series

    Pump fault / drive fault
    F0120
    F0121
    F0122
    F0123

    Pump communication / network
    F0130
    F0131
    F0132

    👉 Root cause differentiation happens inside the guide, not via alarm selection.