Overview
F4 on a Miele washer or washer-dryer means the heater bank temperature sensor is open-circuited. It is a technical fault the owner cannot remedy.
Model compatibility
Miele reuses codes across series and model years, so F4 Heater bank temperature sensor open-circuited may mean something different on another appliance or generation. Confirm this against your model’s documentation and record your full model number before acting.