Miele Washer Error Code F4040

The F4040 error code on a Miele washer indicates that the heating system is failing to raise the water temperature at an adequate rate, even though the heater has been activated by the control system. The machine monitors the rate of temperature rise using NTC (negative temperature coefficient) sensors. When the measured temperature increase falls below the expected threshold over a given time period, the control unit triggers F4040 to indicate insufficient heating power. This points to a problem somewhere in the heating circuit or the system that supports it.

The most likely sources of this fault are the heater elements themselves, which can fail partially or fully due to limescale buildup, burnout, or electrical degradation. The relay responsible for switching power to the heater is another common point of failure. If the relay does not close properly, full power never reaches the heating element. Wiring connections along the heating circuit can corrode or loosen over time, causing resistance losses that reduce effective heating output. On steam-capable models, low or inconsistent steam pressure can also contribute to this fault.

Additional components to evaluate include the circulation pump, which must move water past the heater efficiently for accurate temperature readings and effective heat transfer. A sluggish or failing pump can cause the NTC sensors to register a slower temperature rise even if the heater itself is functioning. The NTC sensors should also be tested directly, as a drifting or out-of-range sensor can report artificially low temperatures and trigger this code. Supply fuses and phase integrity at the terminal block should be confirmed as well, particularly in markets using three-phase power.