Display shows OH or OHH and spa shuts down, pumps may run briefly then stop, water feels very hot

Safety first: Do not use the spa when an OH/OHH condition is present. Turn off power at the GFCI breaker and allow water to cool below 100°F (38°C) before further work.

• Remove spa cover: Open or remove the cover to allow heat to escape and speed cooling.
• Verify actual water temperature: Use an independent thermometer to compare with the displayed temperature. If the display is much higher than actual, suspect a sensor issue.
• Check for flow issues: With power restored and water cooled, run the primary pump on low speed. Confirm strong circulation from jets and that the Master Spas circulation pump (if equipped) is running. Weak or no flow can cause heater to overheat.
• Clean filters: Remove all filter cartridges and run the spa briefly. If OH does not return with filters out, replace or thoroughly clean the filters.
• Inspect heater area: Ensure all slice valves are fully open and there are no kinks in hoses leading to/from the heater manifold.
• Check for stuck heater relay: If the heater indicator is on even when the spa is at or above set temperature, the heater relay on the control board may be stuck closed. This requires control pack repair or replacement by a professional.
• Sensor check: If OH persists with good flow and normal water temperature, test or replace the temperature and high-limit sensors as a set.