Display shows OHH and spa shuts down completely, sometimes accompanied by a clicking sound from the control box.

Safety: Turn off power at the breaker immediately. Do not attempt to reset repeatedly without finding the cause.

• Allow spa to cool: Wait until water temperature is safely below 100°F (38°C).
• Inspect high limit sensor: Remove the equipment compartment panel. Locate the high limit sensor on or in the heater tube (often a second sensor next to the main temperature sensor). Ensure it is firmly seated and its wiring is intact.
• Check for dry‑fire risk: Confirm that the spa was not run with low water level or with valves closed that could isolate the heater. Open all slice valves fully.
• Verify circulation: Once cool, restore power and confirm that the circulation pump starts and water moves through the heater before the heater is allowed to energize.

If OHH recurs immediately or the heater energizes without flow, the control board or heater assembly should be professionally tested and likely replaced.