Boiler shows A05, burner blocked, flue gas temperature too high

Safety: Turn off power and gas. High flue gas temperatures can indicate dangerous combustion conditions. Only trained personnel should work on flue systems.

• 1. Inspect flue terminal: From outside, check that the Brötje concentric flue terminal is not blocked by leaves, snow, or debris. Clear any obstruction.
• 2. Check condensate trap and drain: Remove and clean the condensate trap. Ensure the condensate hose is not kinked or frozen. A blocked trap can cause poor heat transfer and high flue temperatures.
• 3. Examine circulation: Confirm that the system pump runs and that radiators or heating circuits are open. Closed valves or a stuck pump can cause overheating of the heat exchanger.
• 4. Clean primary heat exchanger: Remove the burner and visually inspect the Brötje aluminium or stainless-steel heat exchanger. Brush and vacuum any soot or deposits from the fins. For heavy scaling, a professional chemical cleaning may be required.
• 5. Check flue gas sensor: Locate the flue gas temperature sensor on the flue hood or heat exchanger outlet. Inspect wiring and connector. Replace the sensor if readings are clearly incorrect compared to actual temperature.

If A05 recurs after cleaning and basic checks, a full combustion analysis and flue inspection by an authorised Brötje technician is required.