Spa powers on but will not heat; water temperature remains far below setpoint with no error code displayed.

Safety: Turn off power before accessing heater wiring.

• Confirm settings: Verify that the set temperature is above current water temperature and that the spa is not in Economy or Sleep mode that limits heating.
• Check for heat icon: On the topside, confirm that the heat indicator is displayed when heating is requested. If not, review mode settings.
• Inspect circulation: Ensure the circulation pump is running and that there is strong flow at the heater return jet.
• Test heater element: With power OFF, disconnect heater leads and measure resistance. An open or shorted reading indicates a bad heater that must be replaced.
• Board output check (advanced): A technician can test for voltage at the heater terminals when there is a heat demand. No voltage with a good heater suggests a control board fault.