Your boiler's computer cannot talk to the gas valve, meaning it cannot light the flame to provide heating or hot water.

No communication between controller and gas valve – controller not connected or valve damaged

What causes this fault?

This fault occurs when the boiler's main control board loses its electronic link with the gas valve, which acts as the engine's fuel pump. Without this constant digital handshake, the boiler cannot safely release gas to create a flame, so it shuts down as a safety precaution. The most common reason is a loose internal connection or a specific electronic failure within the gas valve itself.