Control panel shows HL or HOT and spa stops heating; pumps may still run.

Safety first: Turn off power at the GFCI breaker before opening any equipment bay panels.

• Step 1 – Reset power: Turn off the spa at the breaker for 5 minutes, then turn it back on. If HL clears and does not return, it may have been a temporary overheat.
• Step 2 – Bleed air from system: If the spa was recently drained/refilled, air may be trapped in the heater. Loosen the union fittings on each side of the heater tube slightly to let air escape until water seeps out, then retighten. Ensure all slice valves are fully open.
• Step 3 – Clean or replace filter: Remove the Nordic filter cartridge and run the spa briefly without it. If HL does not return, the filter was restricting flow. Clean thoroughly or replace with a Nordic-compatible filter.
• Step 4 – Check circulation pump: Confirm the circulation pump (if equipped) is running when the spa calls for heat. Listen for pump noise and feel for water movement at the heater return. If the pump is hot to the touch but not moving water, it may be seized.
• Step 5 – Inspect high-limit sensor: With power off, locate the high-limit sensor on the heater tube of the Nordic control pack. Check for corrosion, loose mounting, or damaged wiring. Reseat the sensor connector on the control board.
• Step 6 – Replace faulty parts: If HL trips quickly even with good flow, replace the high-limit sensor. If the problem persists, the heater or control board may be misreading temperature and should be evaluated by a technician.