Your boiler's electronic control systems have stopped talking to each other, which prevents the unit from starting or running your heating and hot water.

No reception by main board Connection fault between main PCB and interface; Faulty interface; Faulty main PCB (processor

What causes this fault?

This fault occurs when the boiler's internal sensors detect a massive temperature difference between the water entering and leaving the unit, usually because the water has stopped moving. The most common reason is a failed internal pump or a heavy buildup of sludge and debris blocking the main heat exchanger. Without proper flow, the water inside the unit reaches a boiling point almost instantly, forcing the system to shut down for safety.