Cakes that dome and crack. Cookies that are pale after the full time. A roast that takes forty minutes longer than the recipe promised. An oven that's off-temperature shows itself in the food long before anyone thinks to check it.
Three things account for most of these cases: the oven needs calibrating, its temperature sensor is wrong, or on a gas oven the igniter is too weak to keep the burner lit reliably. They call for very different fixes, so it's worth figuring out which before you do anything.
Safety first
- •For an electric oven, turn off the breaker before removing any panel or element. Many ranges are hard-wired or plugged into a 240-volt outlet behind the unit.
- •For a gas oven, unplug the range and close the gas shutoff valve before pulling it out or working inside.
- •If you smell gas, don't light anything or touch switches. Leave the house and call your gas utility from outside.
Measure, don't guess
The display tells you what the oven is trying to reach, not what it's actually reaching. An oven thermometer on the center rack tells you the truth.
Set the oven to 350°F and let it preheat. Then wait another 20 minutes, because ovens often signal "preheated" before the walls and racks have caught up. Read the thermometer every few minutes for the next half hour and write the readings down.
You'll see the temperature swing. That's normal: the oven turns its heat on and off to hold an average. What matters is the average of your readings compared with the setting.
- •Average close to the setting, swings moderate: the oven is doing its job. Look at pans, rack position and recipes.
- •Average consistently high or low by a similar amount: a calibration issue or a sensor that's reading off.
- •Oven never gets near the setting, or climbs slowly and drops away: a heating problem, such as a weak igniter, a failing element, or a control fault.
- •Temperature climbs far above the setting and keeps going: stop using the oven. The control may be stuck on.
If it's a steady offset: calibrate
Most ovens with digital controls let you adjust the temperature offset through the settings menu or a button combination. The range is usually limited, typically a few tens of degrees each way. The manual gives the exact method for your model.
Older ovens with a mechanical dial often have a small calibration screw behind the knob, or a movable ring on the back of the knob.
If a modest adjustment brings your thermometer readings in line, you're done. If the oven needs more correction than the control allows, or the offset keeps changing, something is failing.
If calibration doesn't hold: the temperature sensor
Most modern ovens measure temperature with a sensor probe, a thin metal rod sticking into the oven cavity near the top back corner. As the sensor heats up, its resistance rises, and the control reads that to decide when to turn the heat on and off.
A sensor that has drifted, or one whose wiring is damaged from years of heat, makes the oven run consistently hot or cold. Some controls display a sensor error code when it fails completely.
With the power off, you can check it. The sensor is usually held by two screws inside the oven, and its connector sits behind the back panel. Resistance at room temperature should match the value in the service sheet for your model; for many common brands it's roughly 1,000 to 1,100 ohms. A reading far outside that, or one that jumps around as you flex the wire, means a new sensor.
Also make sure the probe isn't touching the oven wall. A bent sensor can read the hot metal instead of the air.
Gas ovens: the igniter question
Many Pittsburgh kitchens cook with gas, and most gas ovens made in the last few decades use a hot surface igniter, sometimes called a glow bar. It isn't just a spark. In most designs, the igniter's electric current also opens the oven's safety gas valve. The igniter has to draw enough current to get the valve open.
As igniters age, they draw less current. A weak igniter will still glow bright orange, which is why it fools so many people, but it may not draw enough to open the valve, or it opens the valve only after a long delay. You'll see:
- •A long wait between turning on the oven and hearing the burner catch with a soft whoosh
- •The oven heats up slowly, then falls below the setting and struggles to recover
- •The igniter glows for a minute or more with no flame at all
- •Occasionally, a small puff when the gas finally lights late
That's a failing igniter. It's one of the most common gas oven repairs and one of the most straightforward. Testing it properly means measuring its current draw, which requires the right meter and access to the wiring, so it's reasonable to leave it to a technician.
If the igniter doesn't glow at all, the fault can be the igniter itself, the wiring, or the control that powers it.
Electric ovens: elements
On an electric oven, look at the bake element on the floor of the oven (on many newer ovens it's hidden under the floor panel) and the broil element at the top. Blisters, a visible break or a spot that glowed bright white before it failed all mean replacement. An element can also fail without visible damage. With the breaker off, a multimeter will tell you.
Many electric and some gas ovens have a convection fan at the back. If the fan doesn't turn in convection mode, heat pools and baking becomes uneven.
Other causes worth ruling out
- •A leaky door seal. Check the gasket for gaps, tears or flattened spots. Heat escaping around the door shows up as smoke-darkened glass or a hot handle.
- •A door that doesn't close fully, from worn hinges or a bent frame.
- •Dark pans and glass dishes, which bake faster and darker than shiny metal.
- •After self-clean. The high heat of a self-clean cycle can be hard on controls and thermal fuses. If the oven stopped behaving after one, mention that when you book.
Getting it looked at
When calibration doesn't fix it, the temperature swings wildly, or a gas burner is slow to light, a technician can test the sensor, igniter, elements, valve and control and give you a repair price before starting. We work on both gas and electric ovens and ranges.
To book, call or schedule oven repair online.