Your boiler is struggling to send the correct message to its gas supply valves, which usually means it cannot light safely.

Control signal for both gas valves

What causes this fault?

This fault occurs when there is a communication failure between the boiler's main brain and the gas valves that let fuel into the burner. It is typically caused by a shortcut in the wiring or a failing circuit board that can no longer send the steady electronic signal required to keep the gas supply open. Because the boiler cannot confirm the gas valves are operating correctly, it shuts down immediately as a safety precaution.