Your boiler system is communicating with multiple other boilers through a shared exhaust pipe, and it has detected a technical configuration error in that connection.

What causes this fault?

This fault occurs when multiple boilers share a single chimney system and are failing to talk to each other correctly. It is usually caused by a poor wiring connection between the units or a conflict in the internal settings that tell each boiler which part it plays in the group. In some cases, a faulty electronic module or a blocked sensor in the exhaust pipe can also trigger this communication breakdown.