Pentair SuperFlo VS Fault 21 — Communication Loss
Fault 21 on the SuperFlo VS indicates the communication link between the keypad (HMI) and the motor control board has been lost. The pump stops and displays "21" on the LCD screen.
This is typically a physical connection problem rather than a component failure — the 5-pin connector between the keypad cable and the drive board has become loose or the cable is damaged.
What Causes Fault 21?
Loose Connector
The most common cause — the 5-pin jacketed cable connecting the keypad to the motor control board has worked loose. This can happen after service work, vibration over time, or thermal cycling.
Damaged Cable
- Pinched or kinked cable during drive cover installation
- Rodent damage to the jacketed wire
- Water intrusion causing corrosion on connector pins
- Physical damage during previous service
Drive or Keypad Failure
Less common — if the connector and cable check out, the keypad or drive board itself may have failed.
Troubleshooting Steps
Step 1: Power Cycle First
- Turn off breaker to pump
- Wait until all keypad LEDs turn off (capacitors discharge — up to 60 seconds)
- Turn breaker back on
- If fault 21 does not return, monitor pump for recurrence
Step 2: Inspect the 5-Pin Connector
- Turn off breaker and wait for LEDs to go out
- Remove the drive top cover (typically 4 screws)
- Locate the jacketed wire running from the back of the keypad to the drive board
- Find the 5-pin connector on the drive board socket
- Press firmly until you feel or hear it click into place
- Reinstall drive cover
- Power on and test
Step 3: Inspect the Cable
With power off and LEDs out:
- Run your fingers along the full length of the jacketed cable
- Look for kinks, cuts, or areas where insulation is damaged
- Check for discoloration or corrosion at the connector end
- Ensure the cable isn't pinched under the drive cover
Step 4: Check for Moisture
Inspect inside the drive cover for:
- Water marks or mineral deposits
- Corrosion on the connector pins
- Signs of condensation
If moisture is present, dry thoroughly before reassembling. Verify the drive cover seals properly when reinstalled.
Replacement Parts
| Part | Part Number |
|---|---|
| Drive/Cover Kit (includes drive board and cover) | 353127 |
| Motor/Drive Assembly (complete replacement) | 353132S |
When to Contact Pentair
Call Pentair Technical Service at (800) 831-7133 if:
- Fault 21 persists after reseating the connector
- Cable shows no visible damage but fault continues
- Drive cover or keypad shows signs of physical damage