Ovens are boxes of moving air and radiating metal. Crowding two trays on a dark sheet in bake mode will brown the bottom and leave the top pale even when the cavity is honest. The same oven can also have a bake element that only glows on one side. You cannot tell which story you are in by one tray of cookies.
Preheat until the oven says it is ready, then wait a little longer if you have been opening the door to “check.”
Airflow in a closed box
Use a center rack when the recipe allows. Leave space at the walls. A pizza stone that lives in the oven soaks heat and changes how the first tray bakes. Convection mode moves air; bake mode does not. Using the wrong mode for a recipe is not a failed control board.
Bake versus what the display claims
An inexpensive oven thermometer on the center rack, after a full preheat, is the honest number. If it sits twenty or thirty degrees off the setpoint on more than one evening, the sensor or the element is in play. If it matches the setpoint and food still looks uneven, look at pans and placement first.
When to stop experimenting
A cavity that never heats, a burning smell, or a door that will not close flush is not a rack-position problem. Gas ovens with an odor stay off. Do not pull a wall oven out of the cabinet to inspect wiring.
