Boiler shows E03 and does not respond to heating demand; no relay click is heard

Safety first: Disconnect the boiler from mains power before removing any covers or touching wiring.

Steps to check:

• Visual inspection: Remove the front cover. Locate the flow temperature NTC sensor on the flow pipe or directly on the heat exchanger. Check for signs of moisture, corrosion, or physical damage.
• Check connections: Ensure the NTC sensor plug is fully seated on the sensor and on the main control board. Clean any oxidized contacts with electrical contact cleaner.
• Measure resistance (for advanced users): With power off and sensor disconnected, measure the resistance of the NTC sensor using a multimeter. Compare the reading to the Kospel service chart (typically around 10 kΩ at 25°C, but verify for your model). Infinite or near-zero resistance indicates a faulty sensor.
• Dry and reseal: If moisture is present, dry the area thoroughly and check for leaks from nearby fittings. Replace any damaged gaskets or O-rings.
• Replace if necessary: If the sensor is out of specification, replace it with a genuine Kospel NTC flow sensor and clear the error by cycling power.

When to call a technician: If you cannot access the sensor safely or do not have a multimeter, contact an authorized service center.