The most reliable way to tell whether an oven's heating element has failed is to place a separate oven thermometer inside and compare the reading to the dial setting; if an oven set to 180°C only reaches 140-150°C, the element is probably not running at full power. Food that keeps coming out undercooked, or browns unevenly on one side, points to the same problem.
What do the baking results tell you?
When the bottom element fails, the base of cakes or pastries comes out less cooked than usual while the top looks normal. When the top (grill) element fails, the opposite happens: the top won't brown while the bottom cooks as expected.
If the oven takes much longer than usual to reach its set temperature, or never quite gets there, that's also a sign the element has lost power; recipes start needing longer cooking times than before.
Checking the element visually
With the oven off, cooled down and unplugged, the surface of the element can be examined; blistering, cracks or a visible break mean the element has failed and needs replacing. In some ovens the element should glow faintly while heating; one that never changes colour while heating is usually dead.
Sparks coming from the element, or a burning smell, is a safety warning that needs no waiting around — the oven should be switched off and unplugged immediately and a technician called.
When to call in a technician
If the thermometer shows a big gap, the element has visible damage, or the oven doesn't heat at all, there's nothing left to fix at home; the element is usually an easily replaceable part, but working inside a live electrical appliance is risky, so that job is best left to a technician.
If the oven is still under warranty, an unauthorised repair attempt can void it; contacting the manufacturer or an authorised service centre first is the safest route in that case.
What if the temperature is right but baking is still uneven?
In some cases the element may be working at full power while the hot air inside the oven still distributes unevenly; this is usually down to a failing fan in fan-assisted ovens and is a separate issue from the element. Whether the fan is running can be checked by watching or listening through the oven door while it heats.
A similar symptom shows up when the door seal wears out and stops sealing properly: the oven loses heat, so the thermostat kicks in more often and cooking takes longer. In that case the problem isn't the element but the door gasket, and replacing it is usually a cheaper fix.
Most oven manuals include a calibration or temperature-adjustment option; on some models the thermostat can be nudged by a few degrees by the user. That setting won't fix a failed element, but it can temporarily offset a small, consistent gap, for instance a reading that's always 10°C low.
A build-up of grease and residue blocking the perforated vent at the back of the oven can create a similar temperature imbalance; keeping that vent clean regularly helps both the element and the fan last longer.
The cost of replacing the element varies by oven brand; on some models the part itself is quite cheap, while on certain built-in ovens the labour cost can exceed the price of the part. That cost difference is worth weighing when deciding between a repair and a new oven.