Safety first: Isolate the oven from mains power before removing any panels.

Test all heating elements: Set the oven to different modes (conventional, grill, fan plus) and observe which elements glow or heat. If one element never heats, remove power and test its resistance with a multimeter. Replace any element that is open or significantly higher resistance than specification.
Check convection (fan) heater: On Miele ovens with a rear circular heater, remove the rear inner panel to access the fan heater. Inspect for breaks or hot spots. Test with a multimeter and replace if open.
Inspect wiring and connectors: Loose or burnt connectors to any heater can cause reduced heating. Tighten or replace terminals as needed.
Control board output: If all elements test good, the control board may not be supplying full power. This typically requires replacement of the electronic control module by a technician.

After repair, verify preheat time and temperature with an oven thermometer.

Oven does not reach set temperature; very long preheat times or undercooked food.

Possible Causes