E04 error code appears and the heater will not operate; spa may shut down shortly after starting.

Safety first: Unplug the spa and allow the water to cool below 35°C (95°F) before working on it. Do not remove covers while the unit is hot.

• Check water temperature: Verify with an external thermometer. If water is genuinely too hot, leave the cover off and allow it to cool naturally.
• Inspect filters and flow: Remove and clean the filter cartridge. Ensure strong water movement from the outlet when the pump is running. Poor flow can cause localized overheating.
• Relocate pump/heater unit: Ensure the unit has adequate ventilation and is not in direct sun or enclosed in a tight space. Overheating electronics can trigger E04.
• Reset after cooling: Once water has cooled, plug the spa back in and clear the error by pressing the reset or power button as per the user manual.
• Monitor operation: Run the heater while observing flow and temperature. If E04 reappears quickly, the high-limit sensor or heater control circuit may be faulty.

Warning: Do not attempt to bypass thermal cutouts or high-limit sensors. These are critical safety devices to prevent scalding and fire risk.