Your boiler is currently stuck in a professional service mode used by engineers when they are replacing an internal valve.

Service mode / Diverter valve actuator replacement sequence step

What causes this fault?

This fault occurs when the boiler is manually placed into a specific testing mode used for replacing the motorized valve that switches between heating and hot water. It usually happens if an engineer has left the setting active by mistake or if the main control board has developed a software glitch that keeps it stuck in this maintenance sequence. Because the boiler believes it is being repaired, it will pause normal operation until the sequence is finished or cancelled.