AF failure of wall-hung boiler may cause the heating system to fail to work normally, thus affecting the supply of heating and hot water. This failure is usually caused by the following reasons:

1. Oil pump failure: If the oil pump of the wall-hung boiler fails, the fuel will not flow into the combustion chamber normally, resulting in the failure of the combustion system.

2. Spark plug problem: Failure of spark plug in combustion chamber of wall-hung boiler may also lead to AF failure. This will lead to abnormal combustion of gas and failure of heating system.

3. Windshield failure: If the windshield is improperly installed or fails, the gas cannot flow through the combustion chamber and chimney correctly. This will also lead to the failure of the heating system.

4. Valve problem: Sometimes, the valve of the wall-hung boiler may fail or be damaged. This will cause the heating system to be unable to control the airflow and fuel flow, which will lead to AF failure.

In order to repair AF fault, it is best to ask professional wall-hung boiler maintenance personnel to check. They can accurately determine the cause of the failure and make necessary repairs and hardware replacement. Only professionally trained wall-hung boiler technicians can ensure safe and reliable maintenance. Please avoid DIY maintenance.