Your boiler has detected an internal communication failure between the main control board and the gas valve, meaning it cannot safely light the flame.

Main PCB gas valve control fault

What causes this fault?

This fault occurs when the boiler's main computer loses the ability to send or receive signals from the gas valve, which is the component that controls the flow of fuel. The most common reason is an electronic failure within the circuit board itself or a loose connection in the internal wiring. Because the boiler cannot confirm it can safely control the gas supply, it shuts down as a safety precaution.