Control panel shows OH or OHH, spa shuts down, pumps may run briefly to cool water, topside may flash an overheat warning.

Safety first: Turn off power at the GFCI breaker. Do not use the spa until the cause is identified.

• Remove spa cover: Allow the spa to cool naturally by removing the cover and exposing the water to air. This can take several hours.
• Verify actual water temperature: Use an independent thermometer to compare actual water temperature to the displayed temperature. If the display is much higher than actual, the temperature or high-limit sensor may be faulty.
• Check filtration cycles: In hot weather, long filtration/heating cycles can cause overheating. Once cooled and powered back on, reduce filtration duration in the Aquaterra Spas control settings if possible.
• Inspect circulation: Ensure the circulation pump is running and that there is strong flow from the heater return. Poor flow can cause the heater area to overheat even if the spa water feels normal.
• Reset after cooling: After the water has cooled below 100°F (38°C), restore power and see if the OH code clears. If it returns quickly, the high-limit sensor or control board heater relay may be defective.

Persistent OH errors, especially if the water is not actually hot, require testing of the temperature and high-limit sensors and the control board. Contact a qualified spa technician.