Your boiler is struggling to start because the internal fan is not spinning at the correct speed required for a safe ignition.

Heat exchanger antifreeze active, as fan speed variation is too high. Appliance is within the waiting time of the operation block function

What causes this fault?

This fault occurs when the boiler's control system detects that the fan is not reaching the specific speed required to safely clear gaseout fumes before ignition. The most common reasons are a physical blockage in the fan's blades, a failing motor, or a communication error where the main circuit board cannot read the fan's speed correctly. Without the fan spinning at the exact programmed rate, the boiler will refuse to light as a safety precaution.