Your boiler's burner has encountered a serious ignition or combustion failure, meaning it cannot safely light to provide heat or hot water.

Burner – Propane Aeromatic, Ref. AC 23/05 3585

What causes this fault?

This fault occurs when the boiler attempts to ignite but fails to establish or maintain a stable flame. The most common reasons include a blockage in the burner assembly, a faulty gas valve preventing fuel flow, or worn-out ignition electrodes that can no longer create the required spark.