AO Smith variable-speed pool pump attempts to start, then shuts down with “ERR3” on the display.

Safety First: Turn OFF power at the breaker and lock it out if possible. Do not work on the pump while it is energized.

• Check for hydraulic blockage: Close valves, remove pump lid, and inspect the strainer basket. Clear leaves, stones, or debris. Reach into the volute (with power OFF) and feel for obstructions around the impeller.
• Spin the shaft: Remove the rear motor cover or fan shroud. Try to rotate the motor shaft or cooling fan by hand. It should turn smoothly. If it is stiff or locked, the bearings or impeller may be seized.
• Verify valve positions: Ensure suction and return valves are open to normal operating positions. Running dead-headed (discharge closed) can overload the pump.
• Restart at lower speed: Restore power and try starting at a lower RPM setting. If it runs at low speed but trips at high speed, mechanical drag or winding issues are likely.
• Inspect motor windings: If the shaft spins freely but ERR3 persists, a technician should test winding resistance and insulation. A shorted stator will require motor replacement.