Your boiler thinks it sees a flame before it has even started the ignition process, which is a safety conflict that prevents it from running.

Flame On Before Gas Valve On

What causes this fault?

This fault occurs when the boiler's internal sensors detect a flame signal even though the gas valve hasn't been told to open yet. The most common reasons are a damaged flame sensing electrode that is sending a false signal, a gas valve that is leaking slightly, or a glitch in the main circuit board's electrical logic.