Display shows HL or OH and spa shuts down circulation and heater; water may be very hot near heater.

Safety first: Turn off power at the GFCI breaker. Do not use the spa until the overheat condition is resolved.

• Remove cover and cool water: Open the spa cover to allow heat to escape. Let the water cool below 100°F before further work.
• Check water level and filters: Ensure the water level is above all suction fittings. Remove the Marquis filter cartridges and run the spa (after restoring power) briefly without filters to see if HL clears. Dirty filters are a common cause of low flow.
• Bleed air from system: With power OFF, loosen the union on the circulation pump discharge or on the heater inlet slightly until water seeps out, then retighten. This helps remove trapped air that can cause localized overheating.
• Verify circulation pump operation: Restore power and observe the circulation pump (often a small, continuous-duty pump). You should feel vibration and see water movement in the spa. If the pump is silent or hot to the touch, it may be seized or failed.
• Inspect for scale or debris: If your water is hard, scale can build up in the heater tube and restrict flow. With power OFF and water drained below equipment, remove heater unions and inspect for heavy scale or debris. Clean or replace as needed.
• Reset and monitor: After correcting flow issues, power cycle the spa and monitor temperature. If HL returns quickly and water is not actually hot, the high-limit sensor or control board may be faulty.

Warning: If you suspect a stuck heater relay (heater stays on even when spa is off), disconnect power immediately and contact a technician. This is a fire and scalding hazard.