Heater shuts down with E03, often shortly after ignition or during operation.

Safety: Turn off power to the heater and pump before working on the plumbing.

• Verify pump operation and flow: Ensure the pool pump is running and primed. Check for air in the pump basket and correct any suction leaks.
• Clean filtration system: Backwash or clean the filter, empty skimmer and pump baskets, and remove any obstructions in the suction lines.
• Check valves and bypass: Confirm that all valves leading to and from the heater are fully open. If a manual bypass is installed, set it according to Pentair’s heater installation guidelines.
• Inspect the pressure switch: Locate the water pressure switch on the inlet manifold. With power off, remove the wires and check for continuity when the pump is running (you may need a technician and a multimeter). If the switch does not close with good flow, replace it.
• Look for scale or debris in the header: If flow is good but E03 persists, the internal heat exchanger or header may be restricted by scale or debris and should be inspected by a professional.