Your boiler has encountered a permanent safety lockout and has stopped working to protect itself.

Final fault, e.g.: primary NTC, water pressure, fan/flue problem, ignition/lockout problem

What causes this fault?

This fault occurs when the boiler's internal safety sensors detect a critical issue that prevents safe operation, such as the system losing water pressure or the burner failing to light correctly. It acts as a final safety barrier, often triggered by a failing temperature sensor or a hardware component like the fan or ignition system reaching the end of its life.