Pentair WhisperFlo VST Fault 19 — Motor Start Failure
Fault 19 on the WhisperFlo VST indicates a motor start failure, which could indicate a locked rotor condition. The drive attempted to start the motor but could not get it rotating — either because something is mechanically preventing it, or because the motor itself has failed to start.
This fault is unique to the WhisperFlo VST and does not appear on the SuperFlo VS. The first diagnostic step is always to check whether the rotating assembly can be freed before resorting to disassembly.
What Causes Fault 19?
Locked Rotor — Debris in Impeller
The most common cause. Debris lodged in the impeller prevents the motor shaft from turning when the drive attempts to start. Large leaves, plastic bags, and accumulated scale are common culprits.
Debris in Fan
Debris packed into the fan at the rear of the motor can seize the fan and prevent the shaft from rotating freely. The fan shares the same shaft as the impeller, so a seized fan means the motor cannot start.
Locked or Seized Bearings
If the pump has sat idle for an extended period or ran dry, motor bearings can corrode or seize. This prevents the shaft from rotating even with no impeller obstruction.
Damaged Motor Windings
Less common — internal motor failure preventing start. Typically requires motor replacement.
Troubleshooting Steps
Step 1: Power Cycle
- Turn off breaker to pump
- Wait until all keypad LEDs turn off
- Turn breaker back on and attempt restart
- If fault 19 does not return, monitor for recurrence
Step 2: Check and Clear the Fan
- Turn off breaker — wait for LEDs to go out
- Go to the rear of the motor and locate the fan cover
- Inspect the fan through the fan cover — look for leaves, debris, or buildup
- Remove any debris visible through the fan cover openings
- Use compressed air to blow out any remaining debris
Step 3: Free the Shaft with a Hex-Key
The manual specifically recommends this technique for fault 19:
- With power off and LEDs out, locate the fan cover opening at the rear of the motor
- Insert a hex-key (Allen wrench) through the fan cover to engage the motor shaft
- Gently rotate the shaft back and forth to break up any impeller blockage
- Do not force the shaft — if it won't move at all, proceed to pump disassembly
- If the shaft rotates freely after this step, restart the pump and test
Step 4: Disassemble and Clear Impeller
If the shaft cannot be freed through the fan cover:
- Turn off power at breaker and verify LEDs are out
- Remove drain plugs and drain pump
- Separate the pump halves (volute from rear sub-assembly)
- Remove the diffuser
- Remove and inspect the impeller — clean all debris from impeller vanes and volute passages
- Inspect impeller for cracks or damage — replace if damaged (P/N 073130)
- Inspect the shaft seal for damage while disassembled
- Reassemble and test
Step 5: Inspect for Bearing Failure
If the impeller is clean but the shaft still won't rotate freely:
- Attempt to rotate the shaft by hand — it should turn with moderate resistance
- Grinding, grating, or completely seized rotation indicates bearing failure
- Bearing failure requires motor replacement
Replacement Parts
| Part | Part Number |
|---|---|
| Impeller | 073130 |
| Shaft Seal PA-7 | 071734s |
| Shaft Seal — Ozone/Salt Resistant | 071732s |
| Motor | 356286s |
| Motor/Drive Assembly | 356289s |
When to Contact Pentair
Call Pentair Technical Service at (800) 831-7133 if:
- Fault 19 persists after clearing debris and freeing the impeller
- Motor shaft cannot be rotated after disassembly
- Other faults appear alongside fault 19