Zodiac pool heater displays E05; heater will not start or shuts down quickly.

Safety: Turn off power and gas. Exhaust gases are hazardous; do not operate the heater with a suspected vent blockage.

• Inspect exhaust outlet: Check the flue terminal for nests, leaves, or debris. Remove any obstructions. Ensure vent cap is intact and not crushed.
• Check clearances: Verify that there is adequate clearance around the heater and vent per Zodiac installation instructions. Do not store items against the heater.
• Examine flue sensor: Locate the flue temperature sensor on or near the exhaust collector. Inspect wiring for damage. With power off, test the sensor resistance and compare to Zodiac specifications; replace if out of range.
• Look for soot: Remove the burner access panel and inspect for heavy soot or discoloration, which indicates poor combustion. If present, stop using the heater and have a professional clean the heat exchanger and check combustion.
• Reset and test: After clearing obstructions and verifying the sensor, restore power and gas and test. Persistent E05 requires professional diagnosis of combustion and venting.