| F.26 | Fault: gas valve not functioning | The stepper motor/gas valve body (S1043900) is not operating or is disconnected, so it does not open/modulate. Check with service actuator test, continuity of the harness, and resistance of coils/stepper in the valve. |
| F.27 | Safety shutdown: incorrect flame detection | The gas solenoid valve may become non-tight and allow gas to pass with the burner off, causing a flame signal out of sequence. Check the valve's tightness (bubble test/pressure drop) and ensure the flame disappears when the control board is turned off. |
| F.56 | Fault in the regulation of the circulating flow sensor | The gas valve assembly may improperly regulate the flow (defective mechanism/cable harness), causing an air-gas discrepancy. Check diagnostic readings of the MFS, continuity of the wiring to the valve, and the valve's response to the control board. |
| F.61 | Gas valve activation error | Short circuit/ground in coils or internal defect of the gas valve prevents its activation. Check control voltage from the PCB, insulation/ohmage of coils and wiring harness; replace the valve if there is a leak or coils are shorted. |
| F.62 | Gas valve fault. Disconnection delay | The valve remains stuck or non-tight and does not close in time after the stop command. Verify that the gas flow ceases when the control is cut (downstream manometer/tightness test) and that the flame signal disappears without delay; replace if there is a leak/blockage. |
