Boiler shows E06; hot water temperature is unstable or boiler will not fire for DHW.

Safety: Turn off power and close the cold water isolation valve to the boiler if removing any DHW components.

• Check DHW temperature reading: On models with diagnostic menus, compare the displayed DHW temperature with actual tap temperature. Large discrepancies indicate sensor issues.
• Inspect DHW NTC: Locate the DHW NTC on the domestic hot water outlet or plate heat exchanger. Ensure it is firmly clipped to the pipe or inserted in its pocket and that the connector is secure.
• Check for scale: Heavy limescale on the DHW outlet or plate heat exchanger can cause local overheating and sensor stress. Descale the DHW circuit if necessary.
• Test sensor (technician): Measure resistance of the DHW NTC and compare with CTC temperature/resistance chart. Replace the DHW NTC if readings are out of tolerance.