If your cookies burn on the bottom or a roast needs an extra forty minutes, your oven may not be heating to the number on the display. An oven temperature that is not accurate is one of the most common complaints we hear, and you can usually confirm it yourself before booking a repair.

This post is about an oven that heats, just not correctly. If yours will not heat at all, see our separate guide on ovens that will not heat.

First, Know What Is Normal

No oven holds a perfectly steady temperature. The control cycles the element or burner on and off, so the air inside swings above and below the set point.

A swing of around 10 to 15 degrees Celsius either way during a cycle is normal. What matters is the average over time.

1. Test with an Oven Thermometer

The display cannot tell you if the oven itself is wrong. Place an inexpensive oven thermometer in the centre of the middle rack.

Set the oven to 180 C (350 F) and let it preheat fully. Wait another 20 minutes, then check the thermometer every 5 to 10 minutes for half an hour, opening the door as little as possible. Average the readings. That number is your oven's real temperature.

Repeat at 220 C (425 F) to see whether the error stays steady or grows as the oven gets hotter.

2. Rule Out the Simple Things

A door that does not close tightly lets heat escape, so check for a torn or flattened door gasket.

Dark and glass pans cook faster than light metal ones. Baking stones and foil on the oven floor block airflow, so take them out before testing.

3. Adjust the Calibration Offset

If your oven is off by roughly the same amount at both test temperatures, you can often correct it yourself. Most modern ranges have an offset setting for this.

On many digital controls, you hold the Bake button (or a combination of buttons) for several seconds until an adjustment number appears, then change it in small steps. Older dial ovens may have an adjustment screw on the back of the knob. Your owner's manual has the exact steps.

After adjusting, run the thermometer test again to confirm.

4. Check the Temperature Sensor

Most ovens use a temperature sensor, a thin metal probe mounted near the top of the back wall inside the oven. It reports the temperature to the control. If it is bent against the oven wall, damaged, or failing, the readings drift and the oven overshoots or undershoots.

With the oven off and cool, take a look. The probe should stand clear of the wall. Testing it properly means disconnecting it and measuring its resistance with a meter, which is a job for a technician.

5. Watch for Weak Heating Parts

An electric oven that runs cold and slow may have a bake element that is starting to fail. On a gas oven, a weak igniter can delay the burner lighting on each cycle, so the oven runs well below the setting.

These repairs involve wiring or gas connections, so call for service rather than removing panels. If you smell gas at any point, turn the oven off, leave the house and call your gas utility from outside.

6. Know When the Control Is the Problem

If the temperature is far off or does not respond to the offset adjustment, the electronic control may be at fault. Error codes point the same way. A proper diagnosis saves you from buying a board you did not need.

Get Your Oven Back on Target

If the thermometer test shows your oven is off by more than a small offset can fix, or the sensor or elements look suspect, we can help. Al's Appliance provides in-home oven repair in Kitchener and oven repair in Guelph, plus stove repair in Kitchener, Waterloo and Cambridge.

Call 519-824-8828 or visit alsappliance.ca to book. With Thanksgiving a week away, it is a good time to get your oven baking true again.