Boiler shows E03 and will not operate; internal temperature reading is abnormal or missing.

Safety first: Disconnect power at the main isolator before removing any covers.

• Locate the NTC sensor: On Elnur electric boilers, the primary NTC is usually clipped or inserted into a pocket on the flow pipe or heat exchanger. Refer to the boiler's wiring diagram inside the front cover.
• Check wiring and connector: Inspect the sensor leads for damage, burns, or loose plugs at the PCB. Reseat the connector firmly.
• Test the sensor (if you have a multimeter): With the sensor disconnected, measure resistance across the NTC terminals. Compare to the resistance/temperature chart in the service manual (e.g., around 10 kΩ at 25°C, depending on model). Infinite or near-zero resistance indicates a faulty sensor.
• Check sensor seating: Ensure the sensor is fully inserted into its pocket and has good thermal contact. Refit any retaining clips.
• Replace if faulty: If readings are out of range or intermittent, replace the NTC sensor with the correct Elnur part number.
• Restore power and test: After replacement, power up the boiler, clear the error (if required), and verify that temperature readings are stable.