E05 displayed and the heater does not operate; spa may run bubbles and filtration normally.

Safety first: Disconnect power and verify there is no residual water around the control box before opening it.

• Visual inspection:
  • Locate the heater tube assembly attached to the control box.
  • Check for burn marks, melted insulation, or signs of overheating.
• Check heater connections:
  • Ensure the heater's spade or screw terminals are tight and corrosion-free.
  • Reseat any plug connectors between the heater and PCB.
• Basic continuity check (for skilled users):
  • With the spa unplugged, use a multimeter set to ohms across the heater terminals.
  • A very high or infinite reading indicates an open heater element or internal thermal fuse.
• Replace heater assembly:
  • If the heater is open or visibly damaged, replace the complete Avenli heater tube assembly rather than attempting to repair the element.
  • Transfer any sensors or gaskets as required, following manufacturer orientation.
• If heater tests good: The fault may lie in the main control PCB heater relay. In that case, replace the control box assembly or have it serviced by a qualified technician.