F8 code appears; spa may overheat or shut down unexpectedly during long filter or heat cycles.

Burn and shock risk: Water and components may be very hot. Turn off power at the breaker and allow the spa to cool before working on it.

• Remove cover and cool water: Open the spa cover to allow heat to escape. Do not add cold water rapidly to extremely hot water to avoid shell stress.
• Check water flow: After cooling and restoring power, verify that the circulation pump runs and that there is steady flow from the circulation return. Clean the filter if flow is weak.
• Inspect suction fittings: Ensure that suction grates and skimmer are not blocked by debris, toys, or leaves.
• Check for stuck heater: If the heater indicator remains on even when the set temperature is reached, the heater relay may be stuck closed. This requires control board service or replacement.

If F8 recurs frequently, have a technician test the high-limit sensor and heater relay and verify proper flow rates through the heater.