Ensure the two wires leading to the top of the boiler are snug. Vibration from the pump can occasionally jiggle these loose over time.
In rare cases, the main printed circuit board (PCB) is failing to process the temperature data correctly. Step-by-Step Troubleshooting and Solutions krups error code 09
If you’ve performed Steps 1-4 and the error persists, you likely have a hardware failure. The most common culprits are: Ensure the two wires leading to the top