Your boiler has detected a system error or internal failure that is preventing it from starting up correctly.

If regular resetting is required or appliance still does not operate, investigation is necessary.

What causes this fault?

This fault occurs when the boiler's internal computer, the Printed Circuit Board, suffers an electrical failure or loses communication with its sensors and switches. The most common reason is age-related wear to the board's components or loose connections in the wiring that prevent the boiler from performing its safety checks.