Your boiler has detected a temporary internal communication error or a potential problem with the fan or air supply that may reset itself or require a manual restart.

Temporary fault code (Refer to section 7.10)

What causes this fault?

This fault occurs when the boiler's internal computer system loses track of the fan's speed or the air flow required for safe combustion. It is often caused by a buildup of dust in the fan assembly or a loose electrical connection that disrupts the signal between the components. While it may start as an intermittent glitch, it usually points to a mechanical part that is beginning to fail.