Pentair WhisperFlo VST Troubleshooting Guide
The Pentair WhisperFlo VS/VST is a high-performance variable speed pump widely installed in residential and light commercial pools. It shares a familiar 3-speed schedule interface with Quick Clean mode, and adds RS-485 automation integration alongside the standard low-voltage digital inputs.
This guide covers all WhisperFlo VST fault codes, common field problems, and step-by-step troubleshooting procedures based on the official Pentair installation and user manual.
Understanding WhisperFlo VST Fault Codes
When an alarm is triggered, the drive's LCD display shows a fault code and the pump stops. To clear an alarm:
- Disconnect power at the circuit breaker
- Wait until all keypad LEDs turn off (capacitors discharge)
- Reconnect power
- If the error persists, troubleshoot per the fault code below
WhisperFlo VST Fault Code Reference
| Fault Code | Description |
|---|---|
| 21 | Communication loss between keypad (HMI) and motor control |
| 1A | Power module over current detected |
| 0F / OF | Absolute AC under voltage detected (<99V) |
| 0b / Ob | AC voltage maximum exceeded (>251V) |
| 19 | Motor start failure — possible locked rotor |
| 17 | Phase current offset out of range |
| 16 | Phase current imbalance detected |
| 02 | Absolute phase current limit exceeded |
| 08 | Absolute diode bridge temperature limit exceeded |
| 04 | Absolute power module temperature limit exceeded |
| 06 | Absolute PFC temperature limit exceeded |
| 09 | DC bus over voltage detected |
| 0A | DC bus under voltage detected |
Quick Fault Code Guide
Fault 21 — Communication Loss
Check the jacketed wire on the back of the keypad inside the drive top cover. Ensure the 5-pin connector is fully seated and the cable is undamaged.
Full Fault 21 Troubleshooting →
Fault 1A — Power Module Over Current
If this fault appears repeatedly, inspect the pump's rotating assembly. Disassemble the pump and check the impeller and mechanical seal for damage or obstruction.
Full Fault 1A Troubleshooting →
Fault 0F / OF — AC Under Voltage
Supply voltage has dropped below the 99V minimum. May self-clear if caused by normal utility variation. Persistent faults indicate installation or supply issues.
Full Fault 0F Troubleshooting →
Fault 0b / Ob — AC Voltage Maximum Exceeded
Supply voltage is exceeding the 251V maximum operating limit. The drive shuts down to protect itself from overvoltage damage.
Full Fault 0b Troubleshooting →
Fault 19 — Motor Start Failure
Could indicate a locked rotor. Verify the fan at the rear is clear of debris and attempt to free the impeller before disassembling.
Full Fault 19 Troubleshooting →
Faults 17, 16, 02, 08, 04, 06, 09, 0A — Internal/Temperature Errors
These are UL 60730 self-diagnostic errors. Attempt a hard power cycle first. If the fault persists after multiple restarts, the drive may need service or replacement.
Full Temperature & Internal Fault Troubleshooting →
General Troubleshooting
Pump Will Not Prime
- Air leak: Check suction piping, valve glands, lid gasket, and lid clamp. Ensure lid O-ring is clean and lubricated.
- Low water level: Pool water must be at least halfway up the skimmer opening
- Closed valve: Verify suction valve is fully open
- Dry strainer pot: Fill strainer pot with water before starting after any service
Pump Fails to Start
- No power: Check breaker, GFCI, and wiring connections
- Start/Stop LED off: Press Start/Stop — pump won't run unless this LED is illuminated
- Keypad locked: Hold buttons 1 + Quick Clean simultaneously for 3 seconds to unlock
- External Control Only mode: Press and hold Start/Stop for 10 seconds to toggle off
- Locked shaft: Try rotating impeller through the fan cover with a hex-key; remove any blockage
Pump Runs Then Stops
- Over temperature fault: Check back of pump for dirt and debris; clean with compressed air. Ensure adequate ventilation.
- Over current fault: Pump will automatically restart after 1 minute. If recurring, check impeller for debris and verify voltage.
Reduced Flow or Capacity
- Air pockets or leaks in suction line
- Clogged impeller — disassemble and clean
- Dirty strainer basket — clean regularly
- Dirty filter — backwash or clean cartridges
Pump Is Noisy
- Debris in fan: Clean back of motor with compressed air
- Dirty strainer basket: Remove and clean basket
- Loose mounting: Tighten all mounting bolts
- Cavitation: Check for air leaks on suction side
Pump Runs Without Flow
- Impeller loose or incorrectly installed — verify impeller is secured
- Air leak in suction plumbing
- Blockage in strainer basket, suction line, or discharge piping
- Partially closed valve on discharge side
Programming Reference
Default Schedule
| Speed | RPM | Duration | Start Time |
|---|---|---|---|
| Speed 1 | 3000 RPM | 2 hours | 8:00 AM |
| Speed 2 | 1400 RPM | 10 hours | After Speed 1 |
| Speed 3 | 2200 RPM | 2 hours | After Speed 2 |
Pump Won't Follow Schedule
- Verify Start/Stop LED is illuminated (pump must be "on" to run schedules)
- If in External Control Only mode, the schedule is disabled — toggle off by holding Start/Stop 10 seconds
- Check clock is set — a blinking clock means time needs to be reset (hold Display 3 seconds)
- After a power outage longer than 24 hours, the clock must be reset
Keypad Lockout
To lock or unlock the keypad, press and hold buttons 1 + Quick Clean simultaneously for 3 seconds. The display shows "Loc ON" or "Loc OFF" to confirm.
Factory Reset
To restore factory defaults (does not reset the time of day):
- Stop the pump
- Press and hold buttons 1 + 2 + 3 + Quick Clean simultaneously for 3 seconds
- Display shows "FACt rSt" if successful
- Reprogram schedule and priming speed after reset
External Control (RS-485 and Digital Inputs)
The WhisperFlo VST supports two external control methods:
- RS-485: Serial communication with compatible automation systems (Pentair EasyTouch, IntelliCenter, and third-party controllers). Use RS-485 Automation Wiring Kit P/N 356324z.
- Low-voltage digital inputs: Dry contact signals for external speed selection and start/stop control
When External Control Only mode is active, the on-board schedule is suspended and the pump responds only to external commands. Hold Start/Stop for 10 seconds to toggle this mode.