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Intermatic Support

Why Does My Heat Pump Show an FLO or E3 Code While the Pump Is ON?

Applies To

All ECO, AHN, and Traditional Series Heat Pumps

Question / Problem

Why does my pool heat pump display a FLO or E3 code while the pool pump is running?

Warning: Turn off power to pool equipment at the breaker before opening pump lids, cleaning filters, adjusting valves, or servicing the heat pump. Relieve system pressure and allow moving parts to stop. Never operate the heat pump without adequate water flow. Do not bypass or jumper safety devices.

Common Causes / Conditions

  • The pool pump may be running at a lower speed setting.
  • A dirty filter may be restricting water flow.
  • Valves may be positioned incorrectly.
  • Other possible causes include air in the line or blocked inlets.

Step-by-Step Resolution

  1. Ensure sufficient water flow

    The heat pump requires adequate water flow to operate. If using a variable-speed or dual-speed pool pump, run the pump at high speed or a higher RPM while the heat pump is on.

  2. Clean filtration and baskets

    Inspect and clean or backwash the filter as needed. Empty skimmer and pump baskets to remove debris that may restrict flow.

  3. Confirm valve positions

    Verify valves are positioned so water flows through the heat pump and is not bypassed. Ensure bypass lines are closed during normal heating operation.

  4. Eliminate air and obstructions

    Bleed trapped air from the system and confirm unions and hoses are fully open and not kinked. Check for debris at the heat pump inlet screen if equipped.

  5. Power cycle and recheck

    After making adjustments, turn the heat pump off and back on, then verify whether the FLO or E3 code has cleared.

Tips / Additional Notes

  • If a FLO or E3 code appears while the pool pump is running, verify proper water flow to the heat pump.
  • Increase pump speed or RPM to maintain steady circulation.
  • Clean or backwash the filter and empty skimmer and pump baskets to restore normal flow.
  • Confirm valves are positioned so all water is routed through the heat pump during heating.
  • Remove trapped air or blockages in the plumbing to prevent flow interruptions.
  • Heat pumps operate most efficiently with strong, consistent water flow.
  • If the FLO or E3 code does not clear, contact Intermatic Technical Support or a qualified pool professional.