Your boiler has failed a safety check during its start-up sequence because it cannot identify the gas type or verify the flame correctly.

Gas family check unsuccessful

What causes this fault?

This fault occurs when the boiler's internal computer tries to verify the quality and type of gas entering the system but fails to receive a stable reading. It is physically caused by a mismatch between the gas valve's output and the detection signal from the ignition probes, often due to a components failing to regulate the fuel flow correctly. The most common reason is a malfunctioning gas valve or a faulty control board that can no longer process the flame signal.