F9 displayed, spa may not maintain set temperature or may shut down heater

Safety: Turn off power at the breaker. The heater circuit carries high voltage; do not work on it unless you are qualified.

• Visual inspection: Open the equipment bay and inspect the Villeroy & Boch heater tube and terminals for burn marks, discoloration, or melted insulation.
• Check heater connections: Ensure all heater terminal nuts are tight (do not overtighten) and that wires are not frayed.
• Continuity test (advanced): With power off and wires removed from the heater, use a multimeter to check resistance across the heater element. An open circuit indicates a failed heater.
• Board inspection: Examine the control board heater relay area for signs of overheating or cracked solder joints.

Heater or control board replacement should be performed by a professional due to electrical and scalding hazards.