Your boiler's internal computer parts have lost their identity settings or been replaced incorrectly, meaning the system can no longer communicate with itself to operate.

No valid DSN in display and/or mainboard | Spare part failure display and maiboard interchanged at same time and device specific number not adjusted

What causes this fault?

This fault occurs when the boiler's two main computer boards lose their shared identity or fail to recognise each other. It is most commonly caused by a power surge that wipes the memory settings, or if both internal circuit boards are replaced at the same time without the unique device code being manually re-entered.