F3 error appears and the heater will not turn on; spa may maintain circulation but no temperature rise.

Danger: High voltage present. Turn OFF power at the main breaker and verify with a non-contact voltage tester before touching any wiring.

• Visual inspection of heater: Remove the equipment panel and locate the stainless steel heater tube. Inspect for burn marks, melted insulation, or corrosion at the heater terminals.
• Check heater connections: Ensure all heater terminal nuts are tight and that the wires are not discolored or brittle. Tighten gently if loose, avoiding over-torque.
• Measure heater resistance: With power OFF and wires removed from the heater terminals, use a multimeter to measure resistance across the heater element. Typical values are between 8–15 ohms depending on wattage. Infinite resistance indicates an open heater that must be replaced.
• Inspect control board relays: Look for darkened or cracked heater relays on the Hanscraft control PCB. Burned relays require board repair or replacement.

Because this involves high-voltage heater circuits, if you are not experienced with electrical testing, contact a qualified spa technician to replace the heater or control board.