Why doesn't the oven heat properly, or why does it take so long to heat up?
A guide to the most common reasons an oven cooks unevenly, takes a long time to reach temperature, or never fully heats up, from a burned-out heating element to a miscalibrated thermostat.
Recommended steps:
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Check whether it's one or both heating elements
Most ovens have a top (grill) and bottom (base) element. Turn on each function separately for a couple of minutes and see whether both glow evenly red-hot; if one stays dark, it has burned out.
⚡ Never touch the heating elements while the oven is on or still hot.
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Check the door seal
Run your hand around the door gasket while the oven is on — if you feel obvious heat escaping, the seal may be torn, dislodged, or clogged with food residue, letting heat out and lengthening cook times.
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Test the thermostat with an oven thermometer
Place a standalone thermometer in the center of the middle rack, set 180°C, and compare the actual reading after 20 minutes. A gap of more than 15-20°C points to a miscalibrated thermostat or NTC sensor.
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Clean the fan in convection ovens
In fan/convection ovens, check that the rear fan spins freely and isn't clogged with built-up grease; a sluggish fan distributes heat poorly and creates cold spots.
Frequently Asked Questions
Is it normal for the oven to take 15-20 minutes to preheat?
Yes, that's typical for a home oven at 200°C. If it takes longer than 25-30 minutes or never reaches the set temperature, check the heating elements and thermostat.
Why does one side of the tray brown more than the other?
It's usually a heating element with a weak spot, or a dirty/slow convection fan; rotate the tray halfway through cooking as a temporary fix while you check both parts.