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

Safety first: Turn off gas and power before removing panels or igniters.

Steps to try:

• Check door seal: Inspect the oven door gasket for gaps, tears, or hardened sections. Replace if it does not seal evenly all around.
• Observe flame: During preheat, observe the bake burner flame. It should be strong and even. Short cycling or weak flame suggests an igniter or gas valve issue.
• Replace weak igniter: If the igniter glows but the oven heats slowly, replace the bake igniter; weak igniters are a common cause.
• Verify temperature: Use an oven thermometer to confirm actual temperature vs setpoint. If significantly off, test and replace the sensor if needed.