Blocking fault 4/a/ (2/1/8) - Flow temperature sensor detected over 221°F (105°C)

What does 4/a/ mean?

The flow temperature sensor has detected an extremely high temperature (over 221°F / 105°C) in the system. This is a critical safety shutdown to prevent damage. Heating and domestic hot water are stopped. This is a blocking fault.

• Overheating condition in the boiler
• Poor water circulation
• Faulty flow temperature sensor

Click steps to track your progress.

1. 1

   Press the 'Reset' button on the BC10 basic controller after the boiler has had time to cool.

2. 2

   Check the system pressure and ensure it is adequate.

3. 3

   If the fault reoccurs, contact a qualified service technician to inspect the heating system and sensor.