Your boiler has detected a general internal fault that requires a system reset or power cycle to clear.

Occurs five times per second. Cleared by removing fault and/or main switch off/on.

What causes this fault?

This fault occurs when the boiler's internal computer experiences a communication error or fails to complete its safety checking sequence during startup. The most common reason is an electronic glitch within the main control board or a failure in the ignition process that prevents the burner from firing safely. It effectively means the boiler has reached a 'deadlock' where it requires a manual intervention to confirm the system is safe to try again.