Miele Dryer Error Code F4

Error code F4 on a Miele dryer indicates an open circuit in the fill ring temperature sensor, identified internally as component 1R30. The fill ring temperature sensor monitors the temperature at the drum's fill ring area, which is a critical measurement point for controlling the drying process and preventing overheating. When the dryer's control board reads a resistance value from this sensor that corresponds to a temperature below -5°F (-15°C), it interprets this as an implausibly low reading that is outside the sensor's normal operating range. A reading this far below ambient conditions signals a broken circuit rather than an actual temperature, triggering the F4 fault.

The open circuit condition means the electrical path through sensor 1R30 is interrupted somewhere between the sensor element itself and the control board. This interruption causes the resistance measured by the board to spike to an extremely high or infinite value, which the firmware maps to a sub-freezing temperature equivalent. In practice, this almost never reflects an actual temperature problem inside the drum. Instead, it points to a wiring or connection fault in the sensor circuit.

Diagnosing F4 begins with a physical inspection of the wiring harness and plug connector associated with the fill ring temperature sensor. Technicians should check for broken wires, corroded or backed-out connector pins, and any signs of heat damage along the harness routing. If the wiring and connector are intact and show continuity, the sensor element 1R30 itself should be tested for the correct resistance at a known ambient temperature. A sensor that reads open circuit under normal conditions requires replacement.