Error 06 displayed; water temperature rises rapidly and unit shuts down on overheat.

Safety: Turn off power and allow the heater to cool. Hot water and surfaces can cause burns.

Steps:

• Check system pressure and valves: Ensure all isolation valves on the flow and return are fully open. Verify system pressure is within the recommended range.
• Bleed air: Bleed air from the pump and nearby high points. Airlocks can cause local overheating.
• Inspect the flow NTC sensor: Locate the flow temperature sensor on the outlet pipe or heat exchanger. Check for loose wiring, corrosion, or damage. Clean the sensor tip and ensure it is firmly clipped to the pipe or inserted into its pocket.
• Test sensor resistance (advanced users): With power off, disconnect the NTC and measure its resistance with a multimeter. Compare to Biasi's temperature/resistance chart. Replace if out of range.

Note: If the sensor tests good, the underlying cause is likely circulation or scaling, which may require pump replacement or professional descaling.