Zodiac pool heater shows E18; heater may shut down during operation with no obvious mechanical issue.

Safety: Disconnect power before inspecting internal wiring. Use caution when checking for shorts.

• Inspect for visible damage: Look for burned traces, bulging components, or melted connectors on the control board and relay area.
• Check external loads: If the heater controls an external pump or blower, disconnect those loads and test again. A shorted external device can trigger E18.
• Inspect wiring harnesses: Look for pinched or rubbed-through wires where they pass through metal openings. Repair any damaged insulation.
• Verify fuses: Check any internal fuses for correct rating and signs of repeated blowing. Replace only with the specified type and rating.
• Board replacement: If no external short is found and E18 persists, the main control board may be internally damaged and require replacement.