Spa does not heat; water stays cold or lukewarm even though pumps run and no error code is displayed.

Safety first: Turn off power at the GFCI breaker before testing the heater or sensors.

• Confirm settings: Verify the set temperature is higher than the current water temperature and that the spa is not in economy or sleep mode.
• Check heater indicator: On the topside, confirm that the heater icon or indicator light comes on when heating is expected. If it never appears, the control pack may not be calling for heat.
• Test heater element: With power OFF, disconnect heater leads and measure resistance across the heater terminals. An open circuit indicates a failed element that must be replaced.
• Verify sensor accuracy: Compare displayed temperature with an external thermometer. If the display reads much higher than actual, the temp sensor is faulty and should be replaced.

If the heater and sensors test good but there is still no heat, the control pack’s heater relay or logic may be defective and require professional service.