ApprenticeMedium risk

Pump motor runs but there's no flow

The pump motor runs normally electrically, but there's little or no flow/pressure — the electrics are fine, so the problem is hydraulic, priming, or direction.

Start fault-finding

Safety first

A pump running dry can be damaged quickly. Don't run it dry while investigating. Keep clear of couplings; isolate before mechanical checks.

Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

  1. 1

    Wrong rotation (running backwards)

    Most likely

    Many pumps move little/no flow when run in reverse — a phase-rotation issue after wiring/supply work.

  2. 2

    Loss of prime / air bound

    #2

    A non-self-priming pump that's lost prime, or is air-bound, won't move liquid.

  3. 3

    Closed valve / blocked suction or strainer

    #3

    A shut valve, blocked strainer, or clogged suction starves the pump.

  4. 4

    Mechanical failure (coupling/impeller)

    Least likely

    A failed coupling or damaged impeller means the motor spins but the pump doesn't.

Reports are saved on this device to reflect what you actually find.

Testing sequence

Work through one test at a time. Expected reading and what each result means.

Test 1 of 3
1

Check the rotation direction against the pump's marked direction.

Expected reading

Rotation matches the pump's required direction.

If it passes

Direction correct — check prime, valves, and suction.

If it fails

Running backwards — correct rotation (swap two phases).

Often leads toMotor runs in the wrong directionMotor goes one way but won't go the other (e.g. down but not up)
View all expected readings at once
1. Check the rotation direction against the pump's marked direction.
Rotation matches the pump's required direction.
2. Confirm the pump is primed/not air-bound and that suction valves/strainers are open and clear.
Pump primed, valves open, suction clear.
3. Isolate and check the coupling and (where accessible) the impeller for failure.
Intact coupling driving the pump; sound impeller.

Fault-finding flowchart

The same logic as a decision tree.

  1. 1
    start

    Pump runs, no flow

    → step 2
  2. 2
    decision

    Is the rotation in the pump's marked direction?

    Yes→ step 3No→ step 4
  3. 3
    decision

    Is it primed with suction valves/strainers open and clear?

    Yes→ step 5No→ step 6
  4. 4
    result

    Running backwards — correct rotation (swap two phases).

  5. 5
    result

    Check coupling/impeller — mechanical repair if failed.

  6. 6
    result

    Prime/valve/blockage issue — correct it.

Common mistakes apprentices make

  • Not checking pump rotation after electrical work.
  • Running the pump dry while investigating.
  • Overlooking a closed valve or blocked strainer.
  • Assuming an electrical fault when the motor clearly runs.

When to stop & escalate

Priming, valve, and mechanical (coupling/impeller) issues are for the mechanical/process team. Confirm rotation is correct electrically before handing over.

If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.

Related faults

Motors & overloads

Motor runs in the wrong direction

The motor runs but the wrong way — pump runs backwards, fan blows the wrong way, conveyor reverses. Usually a phase-rotation issue after wiring or supply work.

4 causes3 test steps
ApprenticeMedium risk
Forward / reverse circuits

Motor goes one way but won't go the other (e.g. down but not up)

A reversing drive works in one direction only. One command (say, down) runs fine; the other (up) does nothing, or just hums/trips. Common on hoists, doors, and conveyors.

5 causes4 test steps
QualifiedHigh risk
Motors & overloads

Motor noisy or vibrating (bearing / mechanical)

The motor runs but is noisy, rough, or vibrating — grinding, rumbling, or whining noises that point to bearings or mechanical trouble.

4 causes3 test steps
ApprenticeMedium risk