Display shows OF or OFF and unit will not respond to thermostat changes.

Safety first: No internal high‑voltage work is required for this check, but always keep hands away from live terminals.

• Check mode setting: On the AquaCal control panel, verify the unit is not in OFF or SERVICE mode. Switch to HEAT or AUTO as appropriate.
• Automation system: If connected to a pool automation system (e.g., via AquaCal interface board), check the automation controller to ensure the heater is enabled and the heat demand is active.
• Bypass automation: Temporarily disconnect the external control wires at the AquaCal control board (following the wiring diagram) and set the heater to standalone operation. If it now runs, the issue is with the external controller or wiring.
• Keypad test: If buttons do not respond or display is frozen, the keypad or display board may be defective and require replacement.