| F.26 | Fault: gas valve not functioning. | The stepper motor/drive of the gas valve is not operating or is disconnected/faulty, so the valve mechanism does not open/close; check continuity of coils, connector, and harness to the PCB and perform output test. |
| F.27 | Safety shutdown: incorrect flame detection. | Non-sealed gas solenoid valve/valve assembly that allows gas to pass when it should be closed, causing a false flame signal; check the valve's seal/closure and ensure the flame extinguishes immediately when demand is cut. |
| F.28 | Start-up fault: ignition failed. | Incorrect or faulty gas valve prevents correct gas supply during ignition; check power supply to the valve during the sequence, adjust/check the condition of the gas assembly, and replace the gas valve if coils are open/blocked. |
| F.56 | Fault in the regulation of the circulating flow sensor. | Defective gas valve causes incorrect air-gas regulation (mentioned by the manufacturer) or fault in its wiring; check the harness towards the valve and the operation/modulation of the gas assembly. |
| F.61 | Gas valve control fault (activation error). | Short circuit/ground fault in the harness to the valve or damaged valve coils; check insulation to ground, coil resistance, and control power supply from the PCB. |
| F.62 | Gas valve fault. Disconnection delay. | Gas valve that closes with delay or is not sealing, maintaining flame signal after cutting gas; check shutdown time, tightness, and replace if closure is not immediate. |
