| F0 | Burner blocked – internal fault. | The PCB/control unit (VBC113) has an internal fault and locks the burner. Check power supply, fuse F4 T2.5A, and connectors; if it persists after the reset, replace/code the board. |
| FC | Burner blocked – fan electrical control (control unit) faulty. | The fan control stage integrated into the PCB fails and the board does not control/read the fan, causing a lockout. Check the wiring and fan signal; if there is no external defect, replace the PCB. |
| Fd | Burner blocked – burner control unit fault. | Fault in the BCU/PCB that manages ignition and flame supervision; the boiler goes into lockout. Check electrodes/cables and possible EMC interferences; if it returns after reset, replace the PCB. |
| FF | Burner blocked – burner control unit fault. | BCU/PCB defect causing repeated burner lockout. After checking electrodes/cables and interferences, if the fault persists after the reset, replace the PCB. |
| E3 | Burner in fault state – fault in the safety chain. | If after checking the thermal limit/wiring the safety chain is correct, detection by the PCB may be the cause; replace the control board if necessary after testing. Confirm safety continuity and rule out false contacts. |
| b7 | Emergency mode – burner control unit fault. | BCU/PCB fault forcing emergency mode. Attempt reset; if it reappears, check power supply and connections; rule out external causes and, if confirmed, replace the PCB. |