Control panel shows HL or HLo, spa shuts down heater and sometimes pumps; water may feel extremely hot near heater outlet.

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

• Check for obvious overheating: Remove the equipment bay panel and carefully feel (when cool) around the heater tube and plumbing for signs of discoloration or melting.
• Restore proper flow: Clean or remove the filter cartridge, open all slice valves, and bleed air from the pump unions. Ensure the circulation pump is running when the spa calls for heat.
• Cool down the spa: Leave the cover open for 30–60 minutes to allow heat to dissipate. After cooling, restore power and see if HL clears.
• Inspect high-limit sensor: Locate the high-limit sensor on or in the heater tube (often a thermistor in a dry well). Check that it is firmly seated and not corroded. Loose sensors can read falsely high.
• Replace sensor if needed: If HL recurs quickly and water is not actually overheated, replace the Arctic Spas high-limit sensor/thermistor.
• Persistent HL: If the heater tube is extremely hot while the spa water is not, suspect a flow problem or a stuck heater relay on the control board. Contact a technician for board and heater testing.