Your boiler's main internal computer has developed a fault and can no longer control the heating system correctly.

Defective control panel.

What causes this fault?

This fault occurs when the boiler's internal computer chips or electrical circuits suffer a hardware failure, meaning it can no longer send or receive instructions to other parts like the pump or gas valve. The most common reason is general wear and tear of the electronic components, or sometimes a power surge that damages the sensitive circuitry on the board.