Boiler shows E05 and will not start. Flow temperature on the display may read very low or very high compared to actual pipe temperature.

Safety first: Isolate power before removing any sensor or accessing the control board. Hot water in the flow pipe can cause burns—allow the boiler to cool.

Step-by-step checks:

• 1. Compare display to reality: Touch the flow pipe carefully (or use an infrared thermometer). If the display shows an impossible value (e.g., -20°C or 130°C when cold), the NTC is likely faulty.
• 2. Inspect NTC wiring: Locate the flow NTC sensor on the flow pipe or heat exchanger. Check that the plug is fully seated on the sensor and that the cable is not damaged or pinched.
• 3. Clean sensor pocket: If the NTC is inserted into a dry pocket, remove it gently and check for corrosion or sludge. Clean the pocket and reinsert the sensor fully.
• 4. Basic resistance check (for skilled users): With power off and sensor disconnected, measure resistance across the NTC with a multimeter. Compare to Viadrus specifications (typically around 10 kΩ at 25°C). Infinite or near-zero resistance indicates a failed sensor.
• 5. Reset and test: After reseating or replacing the sensor, restore power and reset the boiler. If E05 persists, the control board input may be defective and requires professional diagnosis.

When to stop: If you are not comfortable using a multimeter or if replacing the NTC does not clear E05, contact an authorised Viadrus service centre.