Safety first: Turn off power at the GFCI breaker before removing filters or opening unions.

Deep-clean filters: Remove Marquis filter cartridges and soak them in a spa filter cleaner solution per product directions, then rinse thoroughly. Replace if they are more than 1–2 years old or show signs of collapse.
Check for kinks or restrictions: Inspect flexible hoses around the circulation pump and heater for kinks, sagging, or partial collapse.
Inspect circulation pump performance: With power restored, feel the return jets associated with the circulation system. Weak flow compared to normal suggests a failing pump or internal blockage.
Check for scale buildup: If you have hard water, drain the spa and inspect the heater tube interior for scale. Descale or replace the heater if heavily coated.
Monitor during heating: After cleaning and inspection, run the spa and watch for HFL. If it appears only when jets are on high, you may have marginal flow and should consider pump or plumbing upgrades/repairs.

Note: Persistent HFL despite good filters and clear plumbing usually indicates a circulation pump nearing end of life.

Display shows HFL and spa may shut down heater intermittently.

Possible Causes