| F63 | Fault in the main PCB memory | The EEPROM/circuitry of the PCB is corrupted or out of tolerance; if sensors and wiring are correct and the error reappears after a reset, the board is the cause. Check PCB voltages and rule out wiring/display faults before reprogramming or replacing. |
| F64 | Fault in the main PCB / rapid fluctuation of the flow/return sensor | The PCB electronics interpret erratic readings from the NTC due to input/ADC failure; if the NTC and its wiring measure correctly, the cause is the PCB. Confirm with ohmic measurement of the NTC and continuity to the PCB. |
| F65 | Excessive temperature of the main PCB | The internal thermal sensor of the PCB detects overheating due to dissipation failure or the circuit itself; if there is no external overheating, the board is defective. Check ventilation/location and actual temperature; if the fault code appears when cold, replace the PCB. |
| F67 | Flame signal fault on the main PCB | The ionization circuit of the PCB is not correctly processing the flame current; if the electrode, ground, and cable are correct and the signal is stable, the fault is in the control board. Check ionization microamps and continuity to the PCB. |
| F70 | User interface incompatible with the main PCB / incorrect product code | After changing the control board or display, the DSN/coding does not match between the UI and PCB; the board needs parameterization or is of incorrect reference. Verify that the DSN on the display matches the data plate and reprogram according to the manual; if it does not accept, incorrect board. |