Your boiler's internal pump or fan is reporting an incorrect speed setting, which is usually a technical communication error between the internal computer and the parts that move water or air.

What causes this fault?

This fault occurs when the boiler's control board sends a command to the pump or fan but receives a confused or incorrect speed signal in return. It is essentially a communication breakdown where the internal computer cannot confirm that these vital moving parts are spinning at the correct rate to safely manage heat and airflow.