If you have an electric oven, it uses coils to produce heat. It is important to remember that your oven uses two coils to heat up, a bake element that does most of the work on the bottom and a broil element on top. This means if one fails, your oven will be cooler to different degrees.
Typically both your oven temperature and a visual inspection will tell that one of your heating elements is not working. However, it may not be the heating element itself that has gone faulty. It could be other parts of the inner workings. However, as with most appliance parts, the concrete way to tell if your heating element is broken is to test it.
How to Test Your Oven Heating Elements
Start by disconnecting your oven from its electrical source via unplugging it or shutting it off at the circuit breaker. Ensure that the interior of the oven is cool, then begin removing the oven racks. If the malfunctioning heating element is a bake element, you may have to unscrew a bottom panel that covers it.
Once you have full access to the malfunctioning heating element in your oven, you will want to start by unscrewing the mounting brackets that secure it. If you are removing the broil element on the top of your oven tub, be sure to have the coil supported to prevent sudden falls.
Once the mounting brackets are removed, pull the element forward slightly to expose the wires in the back. You can now pull the wires off the ends of the heating element. You may wish to label them for re-installation later. Be sure not to let the wires slip back into the cavity as they will be quite the task to fish back out.
Once you have your oven heating element fully removed, you can test it with a multimeter. Set it to x1 and touch one probe to each of the contacts. If it reads either zero or infinity, you will need to replace your heating element as it is indeed the faulty part.