The display shows HL or HLo, and the spa shuts down the heater; pumps may still run.

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

• Remove and clean filters: Take out all filter cartridges from the Master Spas filter canister. Rinse thoroughly with a garden hose from inside out. For heavily soiled filters, soak in a spa filter cleaner solution and rinse well.
• Bleed air from system: If the spa was recently drained or refilled, an air lock may be present. Loosen the union on the pump discharge or heater inlet slightly until water seeps out, then retighten.
• Check circulation pump: With power restored, verify that the circulation pump is running (you should feel vibration and see water movement at the heater return). Replace the pump if it hums but does not move water.
• Inspect valves: Confirm that all slice valves are fully pulled up or open. A partially closed valve will restrict flow.
• Reset code: After correcting flow issues, power cycle the spa. If HL returns immediately, test the high-limit sensor and replace if faulty.
• Persistent HL with good flow: The heater manifold or control pack may be defective. Contact a spa technician for further diagnosis.