Your boiler is currently stuck in an automated filling process and cannot continue until this is resolved.

Whilst filling is in progress (constant temperature control unit)

What causes this fault?

This fault occurs when the boiler’s automated filling system becomes stuck or fails to complete its cycle, often because the system cannot reach the required pressure. The most common reason is a manual filling valve being left open by mistake or a malfunction in the electronic sensor that monitors the water level. In some cases, the internal control board may be unable to register that the filling process has finished, causing the boiler to halt for safety.