Display shows HL or HLt and spa shuts down or limits operation

Safety: Turn OFF power at the GFCI breaker before working in the equipment bay.

• Verify water level: Ensure the spa is filled to the recommended level indicated in the Michael Phelps Spas owner’s manual.
• Remove and inspect filters: Take out all filter cartridges. Check for heavy debris, collapsed pleats, or oil buildup. Clean thoroughly or replace if worn.
• Check slice valves: Locate the gate/slice valves on each side of the circulation and jet pumps and near the heater. Make sure they are fully pulled up (open). Partially closed valves can cause HL trips.
• Bleed air from heater manifold: Slightly loosen the heater union on the inlet side until air escapes and water begins to seep, then retighten.
• Inspect for kinks or obstructions: Look at the plumbing lines around the heater and circulation pump for kinks, crushed hoses, or debris at suction fittings.
• Restore power and test: Turn the breaker ON, run the pumps, and verify strong flow. Monitor the display to see if HL returns.

If HL continues to trip, the heater or control board may be misreading temperature or overheating internally; professional diagnosis is recommended.