BoilerFaultCodesTechnical description
Fan frost protection function active – air pressure switch fault
What causes this fault?
This fault occurs when the boiler's safety sensor detects extremely low temperatures and tries to run the fan to prevent internal components from freezing, but then fails to confirm that air is moving correctly. The most common reason is that the air pressure switch is stuck or the thin internal tubes have become blocked with moisture or debris, preventing the boiler from verifying that it is safe to operate. Because the system cannot confirm the fan is working during this critical frost protection mode, it shuts down to prevent damage.
This fault is almost exclusively seen during winter or periods of extreme cold when the boiler's automatic frost protection sequence is triggered.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.