Digital Heatrae Sadia unvented cylinder or electric water heater shows E03 and does not heat water.

Safety first: Isolate electrical power and allow the cylinder or heater to cool. Do not work on a pressurised hot system.

Steps to address E03:

• 1. Access the sensor: Remove the front or side cover to access the control area. Locate the NTC temperature sensor inserted into the cylinder pocket or clipped to the heat exchanger.
• 2. Check physical seating: Ensure the sensor is fully inserted into its pocket and secured. A loose sensor can give incorrect readings.
• 3. Inspect wiring: Follow the sensor cable back to the control PCB. Look for cuts, abrasions, or signs of overheating. Reseat the connector on the PCB.
• 4. Basic resistance check (for competent persons): With power isolated, disconnect the sensor and measure its resistance with a multimeter. Compare to Heatrae Sadia specifications at room temperature. An open circuit or near-zero resistance indicates a faulty sensor.
• 5. Replace if necessary: If the sensor is out of specification or damaged, replace it with the correct Heatrae Sadia NTC sensor model. Reassemble, restore power, and test.
• 6. Call a professional: If the sensor tests correctly, the fault may lie in the control PCB, which should be diagnosed and replaced by a qualified engineer.