Your boiler is struggling to match the correct fan speed needed to safely clear exhaust gases, which may lead to the system pausing for safety.

Fan speed target value

What causes this fault?

This fault occurs when the boiler's control board sends a signal to the fan but does not receive the correct speed reading in return. The most common reason is that the fan motor is failing or the electrical connections between the fan and the main circuit board have become loose or damaged. Without the fan spinning at exactly the right speed, the boiler cannot safely manage the airflow required for combustion.