Display shows E05, burner does not light or shuts down; often related to temperature sensor issues.

Safety: Switch off power before accessing the control compartment.

• Locate the DHW NTC sensor: On Chaffoteaux water heaters, the DHW NTC is usually clipped to the outlet pipe or inserted into a pocket on the heat exchanger.
• Inspect wiring and connector: Check the two-core cable from the NTC to the main PCB for cuts, burns, or crushed sections. Reseat the connector on the PCB and at the sensor.
• Measure resistance: With the unit isolated, disconnect the NTC and measure its resistance with a multimeter. Compare the reading to the temperature/resistance chart in the service manual (typically around 10 kΩ at 25°C for many NTCs). If the reading is infinite (open) or near 0 Ω (short), replace the sensor.
• Check for moisture: If there is water or condensation around the sensor pocket, dry the area and correct any leaks before fitting a new sensor.
• Reset and test: After replacing or reconnecting, restore power and run hot water. If E05 persists, the PCB input circuit may be damaged and require replacement.