Zodiac pool heater will not start at all; display is blank or does not light.

Safety: Only work on electrical circuits if you are qualified. Turn off power at the breaker before opening electrical compartments.

• Check breaker and disconnect: Verify that the circuit breaker feeding the heater is on and that any external disconnect is closed.
• Inspect power wiring: Open the heater's electrical junction box and confirm that line and neutral wires are securely connected and not burned.
• Check internal fuses: Locate any fuses on the control board or in-line holders. Replace blown fuses only with the same type and rating. If a fuse blows again, a short is present and must be diagnosed.
• Test transformer output: If equipped, measure low-voltage output from the transformer. No output indicates a failed transformer that must be replaced.
• Control board replacement: If proper voltage is present but the display remains dead, the main control board or display board may be defective and require replacement.