Your boiler has lost its identity settings, meaning the internal computer no longer knows exactly which model it is controlling, which prevents it from operating.

No valid DSN in display and/or main board

What causes this fault?

This fault occurs when the boiler's main control board and the display screen are not compatible or have not been properly introduced to each other. It usually happens after a repair where one of these parts was replaced but the unique software code for your specific boiler model wasn't entered. Without this identity code, the two components cannot communicate and the boiler will not fire up for safety reasons.