Display shows OHH or HH, spa immediately shuts down heater and pumps, water may be extremely hot or only warm.

Safety first: Turn off power at the main breaker immediately. Do not enter the spa if water is excessively hot.

• Verify actual water temperature: Use a separate thermometer to check water temperature. If water is above 104°F (40°C), allow it to cool with the cover open.
• Inspect for dry fire signs: Look at the heater tube for discoloration, burnt smell, or melted insulation, which indicate the heater ran without water flow.
• Check for flow restrictions: Clean or replace the filter, ensure all slice valves are open, and verify the circulation pump is operating.
• Sensor inspection: With power off, inspect the temperature and high-limit sensors on the heater tube. Ensure they are firmly seated and not damaged. Replace if cracked, swollen, or corroded.

If the heater continues to heat with the spa set to a low temperature or when the system should be off, the heater relay on the control board may be welded closed. In that case, the control board and/or heater assembly must be replaced by a qualified technician.