Your boiler has encountered an internal timing error or electrical communication fault because it didn't enter the correct setup mode when its gas control valves were being linked.

Failure to enter the commissioning mode will result in a fault condition being detected when actions are carried out while reconnecting power leads to the RH valve.

What causes this fault?

This fault is physically caused by an electrical communication error between the boiler's control board and the gas valves during a startup or reset sequence. It typically happens when the system fails to synchronise its safety checks, often due to a loose connection or a failing wiring harness that prevents the components from 'handshaking' correctly. In many cases, this indicates that the internal electronics can no longer reliably control the flow of gas, leading the boiler to shut down for safety.