Spa will not heat; water stays cold even though pumps run and set temperature is high

Safety first: Turn off power at the GFCI breaker and verify no voltage is present before opening the control pack or touching heater wiring.

When the spa circulates but does not heat, the heater circuit is suspect.

• Confirm demand for heat: Set the temperature several degrees above current water temperature and ensure the spa is in Standard/Ready mode.
• Check heater indicator: On many American Whirlpool control packs, a heater icon or LED indicates when the heater should be energized. If the icon never appears, the control logic or sensors may be at fault.
• Inspect heater terminals: Remove the control pack cover and look for burnt or loose heater connections.
• Test heater resistance: With power off and wires removed, measure resistance across the heater element. An open circuit or very low resistance indicates a bad element.
• Replace heater assembly if failed: Drain or isolate the spa as needed, remove heater unions and mounting hardware, and install a compatible American Whirlpool heater assembly, reusing or replacing gaskets as required.

If the heater tests good but never receives power, the control board heater relay or sensor logic likely needs professional diagnosis and repair.