Sn2 error and spa may shut down heating or show unstable temperature control.

Safety first: Turn off power at the breaker before working on the heater sensors.

• Locate Sn2 sensor: Identify the secondary sensor (often clamped to the heater tube or in a separate well). Ensure it is firmly attached and making good thermal contact.
• Check connector: Unplug and replug the Sn2 sensor connector on the control board to clean contacts.
• Inspect cable: Look for damage along the cable route. Replace the sensor if any damage is found or if the error persists.
• Test operation: After replacement, restore power and confirm that the Sn2 code is cleared and heating operates normally.