Your boiler's internal computer has encountered a communication error or software glitch that is preventing it from running safely.

Internal error.

What causes this fault?

This fault occurs when the boiler's main control centre suffers a sudden communication breakdown between its internal electronic components. It is typically caused by a component failure on the circuit board or a loose connection in the wiring harness that prevents the computer from verifying its own safety checks. Because the 'brain' of the boiler can no longer guarantee safe operation, it shuts the system down immediately.