An oven that has drifted 40 degrees out of calibration does not look broken. The light comes on, the fan runs, the display says exactly what you set. It just produces dense cakes, dry chicken and biscuits that are black underneath and pale on top.
Most people spend months adjusting recipes before they suspect the appliance.
Test it properly, in twenty minutes
Buy an oven thermometer. They cost less than a takeaway and every kitchen should have one.
Hang it in the centre of the middle rack. Set the oven to 350°F and leave it for a full twenty minutes after the preheat chime, because ovens overshoot and then settle, and reading it too early gives you a meaningless number.
Read it without opening the door if the thermometer is visible through the glass.
Within 15 degrees: normal. Every oven cycles around its setpoint.
Off by 25 to 50 degrees, consistently: the temperature sensor has drifted. This is a common, inexpensive repair, and many ovens also have a user calibration offset in the settings menu that can compensate for smaller errors.
Off by more than 50 degrees, or wandering unpredictably: the sensor, the control board or the element is failing rather than drifting.
What actually causes it
The temperature sensor
A thin probe protruding into the cavity, usually at the back. It reports resistance to the control board, which converts that to a temperature. As it ages, the resistance curve shifts and the board is told a lie.
This is the most common cause of a consistent offset, and it is an inexpensive part.
A failing element
An electric bake element that has developed a hot spot or a partial break heats unevenly. The oven reaches its setpoint at the sensor while the food sees something quite different. Look at the element with the oven cold: blistering, a dull section, or a visible split all mean it needs replacing.
A door that no longer seals
Sagging hinges let the door sit fractionally open, and heat escapes at the top. The classic symptom is food that browns unevenly front to back, and an oven that never quite gets there on a cold day.
Check by closing the door on a strip of paper at several points around the frame. It should grip everywhere.
The convection fan
On a convection oven, a fan that has slowed or stopped removes the even heat distribution the whole design depends on. The oven still heats. It just heats like a much worse oven.
The self-clean warning
Self-cleaning cycles run the cavity up past 800°F. That is hard on door locks, thermostats and the control board sitting behind the fascia, and a meaningful share of oven repairs we attend happen within a day of a clean cycle.
If you use it, run it at a time when a failure would be inconvenient rather than catastrophic. Never the week of a holiday you are cooking for.
See what an oven repair visit covers.
FAQ
Can I just adjust my recipes instead?
For a consistent 25-degree offset, yes, and plenty of people do. But an oven that is drifting will keep drifting, and the same sensor fault often ends with the oven failing to heat at all.
My oven bakes unevenly front to back.
Door seal or hinges first, then the element, then the convection fan if it has one.
The broiler works but the oven does not heat.
Separate circuits and separate elements. That points squarely at the bake element or its relay, and it is good news: you have narrowed it down to one part.
Is a wall oven harder to repair than a range oven?
Not harder, just slower. Wall ovens have to come out of the cabinet, and most are a two-person lift, so we allow more time for them.
We repair built-in ovens, wall ovens and range ovens across our whole service area.
