F.399 — Burner in fault state due to IO electrode ground fault

What does F.399 mean?

This fault indicates a problem with the burner, specifically an IO electrode ground fault or an issue with the burner control unit. The boiler will not function as expected.

• IO electrode ground fault
• BCU burner control unit is faulty

Click steps to track your progress.

1. 1

   Check the IO electrode for any signs of a ground fault or damage.

2. 2

   Reset the boiler by briefly turning off and on its power supply.

3. 3

   If the fault persists, contact a qualified heating engineer, as the BCU burner control unit may need to be replaced.