Thanks for choosing FixYa and welcome to the site. If you have a electric oven or a gas oven that won't heat or doesn't heat properly, here are some things you will need to check. The most likely cause of a oven not heating correctly is a defetive heating element. You have two types of heating elements in your oven. The bottom element(s) are the baking elements. The element(s) on the top are the broil elements. If you don't see the bright red glow from the element, chances are they are not working or not working correctly. If a heating element is bad, you need to replace
the entire element. If your oven is warm and not correctly hot, one of the elements may be bad. In most ovens, when you preheat, both elements are used. This would make the oven to appear like it is working correctly but it is not. If the elements are not working, they might not be getting power. Test the wires to the elements with a voltage meter to make sure they are getting power before you decide to change them out. Many electrical ovens have a sensor that monitors the oven temperture. Ovens that have this sensor usually contain a digital display on the oven. The sensor could be defective. Those without the sensor use the basic mechanical system to control the oven temperature. You also want to check the thermostat sensing bulb. Make sure the bulb is good and has not come loose. Now, if you have a gas range oven that doesn't heat properly, first, you want to check your bake igniter. It may have burned out or it could be not working properly. It will be located near your burner. It is also possible that you are not getting gas to the burner. If so, it may be the gas safety valve or the igniter. You need to check your selector switch and thermostat as well. They may be defective. Always make sure you test the parts for power with a voltage meter of some type before you decide to change the part. If you have a part that appears to not be working, it may not be getting power because of a bad wire or broken connection. Thank you for your time and thanks for choosing FixYa.