Your boiler's internal control system has lost its connection, meaning it cannot properly talk to its own brain to coordinate heating or hot water.

Communication is interrupted.

What causes this fault?

This fault occurs when the boiler's internal computer can no longer 'talk' to the sensors or the thermostat that tells it when to turn on. The most common reason is a loose or damaged wiring connection inside the unit, or a internal failure on the main circuit board itself. This break in communication means the boiler enters a safety mode because it cannot guarantee it is receiving the correct operating instructions.