If you suspect that your oven's thermostat or heating element is failing to bring your oven to the proper temperature, you can use an oven thermometer to check the oven temperature. However, if you do not have an oven thermometer or you are in a hurry and need to know right away, you can boil water in your oven to determine if the oven heats at the temperature you select.
Fill a 4-quart glass container approximately 3/4-full with tap water.
Place the bowel of water into the center rack of your oven.
Set the oven temperature to 215-degrees F. Water boils at 212 degrees F but most ovens only allow for increments of 5 degrees.
Inspect the container of water once the oven warm-up light turns off. If the oven temperature is correct, the water will boil. If the oven temperature is too low, the water will not reach the boiling stage.