F.405 — Burner in fault state due to ionization electrode ground fault

What does F.405 mean?

This fault indicates that the burner is in a fault state, possibly due to a ground fault in the ionization electrode or an issue with the burner control unit. The boiler will not operate as intended.

• Ionization 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.