Oven does not reach set temperature, very long preheat time, undercooked food

Safety first: Isolate the oven from the mains before testing elements or removing panels.

• Test all heating elements: Remove the rear panel. Identify the upper grill element and circular fan element (if present). Disconnect each element and measure resistance with a multimeter. Compare readings to the service manual; an open circuit indicates a failed element. Replace any element that is open or visibly damaged.
• Check fan‑assisted mode: If the oven heats better in conventional mode than in fan mode (or vice versa), suspect the element associated with the problematic mode. Replace the circular element if fan mode is weak.
• Inspect control board relays: If all elements test good, inspect the PCB for cold solder joints or burnt tracks at the element relay outputs. Resolder cracked joints if you are experienced; otherwise replace the board.
• Verify supply voltage: For 3‑phase Brandt built‑in ovens, ensure all phases are present and correctly wired at the terminal block. A missing phase can cause weak heating. This check should be done by a qualified electrician.