Zodiac pool heater displays E03 and will not fire; may occur immediately on a call for heat.

Safety: Turn off power to the heater before opening any panels. Do not run the heater without proper water flow.

• Verify pump operation: Ensure the pool pump is running and fully primed. Check for air in the pump basket and correct any suction leaks.
• Clean filtration system: Backwash the sand filter, clean or replace cartridge filters, and empty pump and skimmer baskets to restore proper flow.
• Check valves and bypass: Confirm all valves leading to and from the heater are open. If a heater bypass is installed, ensure enough flow is directed through the heater.
• Inspect pressure switch: Locate the water pressure switch on the water manifold. Check for loose wires and corrosion on terminals. With power off, remove the switch and inspect the port for scale or debris; clean gently.
• Adjust or replace switch: Some Zodiac pressure switches are adjustable. Following the service manual, make minor adjustments only if flow is known to be correct. If the switch does not close even with strong flow, replace it with a Zodiac-compatible water pressure switch.