Oven takes excessively long to preheat or never reaches set temperature.

Safety first: Disconnect power before testing elements or wiring.

• Check elements/igniter: Observe whether the bake element or burner is operating. For electric, ensure the element glows evenly. For gas, ensure prompt ignition and steady flame. Replace weak elements or igniters.
• Verify convection fan: On convection models, ensure the convection fan motor runs when convection is selected. Replace the motor if seized or noisy.
• Inspect door seal: Check the door gasket for leaks that can let heat escape. Replace if damaged.
• Check supply voltage: Have an electrician verify that the range is receiving full rated voltage. Low voltage will cause slow heating.

Use an oven thermometer to confirm actual temperature versus setpoint during diagnosis.