BoilerFaultCodesTechnical description
Heat exchanger antifreeze active as fan speed variation is too high
What causes this fault?
This fault happens when the boiler's internal computer detects that the fan is not spinning at the correct speed, which triggers a safety pause to prevent the system from freezing up. The most common cause is a blockage in the flue pipe or heavy ice buildup that prevents air from moving freely through the unit. Occasionally, it can also be triggered by moisture or debris interfering with the electrical signals between the fan and the control board.
This fault is much more common during periods of extreme cold when ice can block the external flue or intake vents.
DIY fix possible
Check the external exhaust pipe (flue) for any obstructions like leaves or debrisIf it is very cold outside, check if the white plastic condense pipe is frozen and gently thaw it with warm waterTurn the boiler off and back on again to see if the message clears