Your boiler is temporarily paused because it has detected a potential issue with its internal sensors while performing a self-test.

Flow-/Return-sensor check is running, demand (DHW or heating) is blocked

What causes this fault?

This fault occurs when the boiler performs a safety check and notices that the temperature sensors for the water going out and coming back are giving conflicting or illogical readings. The most common reason is that one of the sensors has developed a fault or is starting to wear out, preventing the boiler from accurately monitoring its own performance. It pauses the heating process to ensure it doesn't overheat or run inefficiently based on incorrect data.