Your boiler's computer brain has lost its settings or is experiencing an electrical fault, preventing the system from starting up.

PCB UNCONFIGURED/FAULTY OR GAS VALVE SHORT CIRCUIT. SEE SECTION 3.19 IF FAULT PERSISTS REPLACE PCB

What causes this fault?

This fault occurs when the boiler's main control board loses its identity or suffers an internal electrical failure, meaning it no longer knows how to safely manage the heating process. It can also be triggered by a faulty gas valve or damaged wiring creating a short circuit that prevents the system from starting. Essentially, the 'brain' of the boiler has become corrupted or disconnected from the components it needs to control.