Boiler shows F.27, ignition attempt aborted

Safety: Isolate power and gas before removing the combustion cover. Only qualified personnel should access the burner area.

• Reset once: Attempt a reset. If F.27 reappears, continue with checks.
• Check for moisture: Look for signs of water ingress inside the combustion chamber or on the electrode assembly. Any leaks from the flue or seals must be repaired by an engineer.
• Inspect electrode (engineer-level): The ionisation electrode can be cleaned gently with fine abrasive pad to remove soot. It must be correctly positioned relative to the burner.
• Check earthing: Ensure the boiler has a solid earth connection at the supply. Poor earth can affect flame sensing.
• PCB diagnosis: If electrode and wiring are sound, the PCB may misread flame current and require replacement by a technician.