Cookies burn on the bottom, a roast takes twenty minutes longer than the recipe says, and the owner blames the oven. Sometimes rightly. But LG ranges and wall ovens are built with an adjustment for exactly this, and before assuming a fault it is worth knowing whether the oven is consistently off, which the adjustment fixes, or inconsistently off, which no setting will cure.
Measure Before You Adjust
A single reading from an oven thermometer proves little, because every oven cycles above and below its set point as the element switches. Put a good oven thermometer on the centre rack, set the oven to 350°F, and let it run for at least half an hour past the preheat signal. Then read the thermometer every few minutes for twenty minutes and average the readings. LG's preheat indicator sounds when the sensor reaches temperature, but the walls and racks take longer to catch up, so a reading taken the moment the beep sounds is not the oven's working temperature.
The Adjustment LG Provides
LG ovens include an oven temperature adjustment in the settings that shifts the whole scale up or down by a set number of degrees; the manual for your model gives the exact range and the button sequence, and it is usually reached by holding the Bake key. If your average is 20 degrees low, set the adjustment 20 degrees high. This is calibration, not repair, and it is the correct answer to an oven that is steadily and predictably off.
Convection Changes the Arithmetic
Many LG ovens automatically lower the set temperature by 25 degrees in convection bake, because moving air cooks faster, and they display the adjusted figure. An owner who does not know this reads the display, thinks the oven is running cold, and compensates twice. Check the convection conversion section of your manual before deciding the oven is wrong.
When It Is Not Calibration
Inconsistency is the clue. An oven that reads 340 one day and 390 the next at the same setting, that overshoots wildly during preheat, or that produces an F code about the sensor, has a temperature sensor drifting out of range, a control relay sticking, or an element that is failing. Look at the bake element during preheat on an electric model: it should glow evenly along its length, and a bright spot or a dead section is a failing element. Check the door gasket for gaps and the door for a sag on its hinges, both of which lose heat unevenly and confuse every reading.
The Repair
The temperature sensor is a thin probe at the top rear of the oven cavity, wired through the rear wall to the control board. It is tested by resistance and replaced with the range disconnected from power at its breaker and moved away from the wall; on a gas range, the gas shutoff valve is closed before the range moves. Elements and relays are reached the same way. None of that is an owner project, because the oven circuit carries 240 volts and the connections sit behind the cavity.
What to Report
Bring the numbers: the set temperature, the averaged reading, whether the error is constant, and whether it is worse in convection or after self-clean. Book an LG oven repair with the model number from the plate behind the door, and the technician can confirm whether the sensor is drifting rather than guess from a description of burnt cookies.