| F.26 | Fault: gas valve not functioning. | The stepper motor/coils of the gas valve (SIT 053462) are open, shorted, or disconnected, so the valve does not operate; check coil resistance/insulation and stepper motor signal/return from the PCB during the ignition attempt. |
| F.61 | Gas valve activation error. | The gas valve cannot be operated due to an internal fault (coils shorted/ground leakage) or wiring failure; confirm by measuring the resistance/insulation of coils, wiring harness, and control signal from the PCB. |
| F.62 | Gas valve disconnection delay. | The gas valve remains stuck/not sealed and takes time to close, maintaining the flame signal after the closure command; check for tightness and closing time (ionisation/analyser) and rule out internal leakage of the valve assembly. |
| F.28 | The appliance does not start: failed ignition attempts during startup. | The gas valve does not open or is incorrectly adjusted, preventing flow during ignition; check inlet pressure, control signal, and actual valve opening during the ignition sequence. |
| F.29 | The flame goes out during operation and subsequent ignition attempts fail. | Intermittent fault of the gas valve (flow drop/leakage when hot) causes flame loss; check pressure stability and valve operation under load and confirm by replacing/adjusting the valve assembly if necessary. |