Pentair WhisperFlo Shaft Seal Leak Repair

A shaft seal leak is one of the most straightforward WhisperFlo repairs — a clear diagnosis, a well-defined procedure, and a low parts cost. The mechanical shaft seal prevents water in the pump volute from reaching the motor bearings and windings. When it fails, water drips or streams from the junction between the motor and the volute, and the motor bearings begin absorbing water immediately.

A failed shaft seal should be repaired promptly. Even a small drip left running for weeks will wick into the front bearing and corrode it, turning a $20 seal replacement into a $150–300 motor replacement.

Identifying a Shaft Seal Leak

The shaft seal sits inside the seal plate (the flat plate between the motor and volute). Water leaking from this seal appears:

• As a drip or stream from the bottom of the joint between motor and volute housing
• As a wet stain or mineral deposit on the motor face or seal plate
• As standing water under the pump pad — directly below the motor/volute junction

Distinguish shaft seal from union leaks: Union leaks appear at the threaded connection points where the plumbing attaches to the pump. Run your finger along each union while the pump runs — water at the union threads is a union leak, not a seal leak. The shaft seal leak location is specifically at the motor-to-volute joint, centered on the shaft axis.

Distinguish from condensation: In humid climates, condensation can form on motor housings. Condensation is distributed across the motor surface; a shaft seal leak drips from the specific joint between motor and volute and leaves a deposit track downward.

Tools Required (from Manual)

• 3/32-inch hex head wrench
• 1/4-inch hex-key wrench (fits motor shaft flats)
• 9/16-inch open end wrench
• Flat blade screwdriver
• #2 Phillips screwdriver
• Non-contact voltage tester
• Replacement shaft seal (see part numbers below)

Shaft Seal Part Numbers (from Manual)

The PA-7 (071734S) and A7 (071728) seals are not interchangeable. Inspect the old seal when removed and match the construction. The complete Seal Plate Kit (P/N 350202) includes the seal plate, gasket, and seal — use it when the seal plate itself is damaged or worn.

Disassembly Procedure

Step 1: Isolate the Pump

1. Turn off the pump at the timer or automation system
2. Turn off power at the circuit breaker
3. Close the suction valve and all discharge valves
4. Open the manual air relief valve on top of the filter to release pressure from the system

Step 2: Drain and Separate the Pump Halves

1. Drain the pump by removing the two drain plugs (P/N 071131) from the housing — store plugs in the pump basket
2. Remove the 6 bolts that hold the strainer pot to the motor/hydraulic sub-assembly
3. Gently pull the two pump halves apart, removing the motor/hydraulic sub-assembly

Step 3: Remove the Diffuser and Impeller Lock Screw

1. Use a 3/32-inch hex head wrench to loosen the two holding screws on the diffuser
2. Hold the impeller securely in place and remove the impeller lock screw using a #2 Phillips screwdriver

Step 4: Remove the Impeller and Seal Plate

1. Using a 1/4-inch hex-key wrench, hold the motor shaft in place at the rear of the motor to prevent the shaft from spinning
2. Remove the impeller screw and washer using the Phillips screwdriver (left-hand thread — loosens clockwise)
3. Remove the impeller from the motor shaft
4. Remove the four bolts from the seal plate to the motor using a 9/16-inch wrench
5. Remove the seal plate from the motor shaft

Step 5: Remove the Old Seal

The shaft seal consists of two parts: a rotating member and a ceramic seal.

1. Remove the spring/carbon rotating member from the motor shaft
2. Use a flat-blade screwdriver to gently pry the ceramic seat out of the seal plate pocket
3. Clean the seal pocket in the seal plate with a clean cloth
4. Inspect the shaft for grooves or corrosion where the seal rides — a grooved shaft will cause a new seal to fail immediately

Installing the New Seal (from Manual)

1. Use silicone sealant on the metal portion of the new ceramic seat before pressing it into the seal plate — be careful to keep sealant off the seal face. Ensure the seal is fully seated and allow 24 hours for sealant to cure. (Complete seal plate with seal replacement kit available, P/N 350202.)
2. Before installing the ceramic section of the seal into the impeller, ensure the impeller is clean. Use light-density soap and water to seat the seal. Press the seal into the impeller with your thumbs and wipe off the ceramic and carbon faces with a clean cloth.

Reassembly (from Manual)

1. Remount the seal plate to the motor by installing bolts in a criss-cross (X) pattern and tightening to 70 in-lbs
2. Clean the motor shaft thread and the impeller insert, then screw the impeller onto the motor shaft
3. Screw in the impeller lock screw counter-clockwise (left-hand thread tightens counter-clockwise) and tighten to 25 in-lbs while holding the motor shaft with the 1/4-inch hex-key wrench
4. Remount the diffuser onto the seal plate — ensure the plastic pins and holding screw inserts are aligned
5. Grease the diffuser O-ring and seal plate gasket (P/N 357100)
6. Grease the bolt threads and assemble the motor sub-assembly to the strainer pot using the two through-bolts for proper alignment. Do not tighten the through-bolts until all 6 bolts are in place and finger-tightened. Torque in a cross pattern to 110 in-lbs
7. Fill the pump with water
8. Reinstall the pump lid and plastic clamp
9. Re-prime the system

Restart and Testing (from Manual)

1. Open suction and discharge valves
2. Remove strainer lid, fill the strainer pot with water up to the inlet port, reinstall the lid — ensure the lid O-ring (P/N 350013) is clean and well lubricated
3. Turn the clamp clockwise until the handles are horizontal
4. Open the manual air relief valve on top of the filter and stand clear
5. Restore power at the breaker and start the pump
6. When water comes out of the air relief valve, close the valve
7. Observe the motor/volute junction — any persistent drip indicates improper seal installation. Shut down and re-inspect

Related Guides

• WhisperFlo Motor Noise Diagnosis
• WhisperFlo Reduced Flow Diagnosis
• WhisperFlo Motor Wiring and Voltage Issues