Oven does not reach set temperature, takes very long to heat or stops below target

Safety first: Disconnect mains power before removing panels or accessing wiring.

• Check door seal: Inspect the De Dietrich door gasket all around for gaps, tears, or hardened sections. Close the door on a sheet of paper; if it pulls out easily in multiple spots, the seal or hinges may need adjustment or replacement.
• Test heating elements: Run the oven in conventional and then fan-assisted modes. If one mode heats better than the other, the corresponding element (upper, lower, or circular fan element) may be weak or open. Test each element's resistance with a multimeter and compare to specifications.
• Check temperature sensor: Measure the NTC sensor resistance at room temperature and again in warm water (~50°C) if removable. Resistance should change smoothly. If readings are out of range or jumpy, replace the sensor.
• Inspect control board relays: Look for signs of overheating or pitted contacts (burn marks) on the heater relays. If the relays are not reliably switching, the main control board may need replacement.
• Calibrate (if available): Some De Dietrich models allow temperature calibration in the settings menu. Use an oven thermometer to adjust offset if the hardware is otherwise sound.