BoilerFaultCodesTechnical description
Antifreeze active – fan speed variation too high – waiting during blocking function
What causes this fault?
This fault occurs when the boiler detects that the internal temperature has dropped low enough to risk freezing, or when the fan cannot maintain a stable speed due to extreme external wind. The system enters a temporary blocking mode to protect the internal components from damage until conditions stabilise. It is often triggered when the air intake is restricted or when cold air is blowing directly back through the flue system.
This fault is most common during periods of extreme cold or high winds, particularly during the winter months.
DIY fix possible
Check that the external condensate pipe has not frozen and clear any ice if necessaryEnsure the external flue terminal is not obstructed by snow, debris, or heavy iceWait for the weather to improve as the boiler will automatically restart once temperatures rise or wind gusts subside