Why Your Oven Is Not Heating to the Correct Temperature
Your cookies burn at a setting that used to be fine. An oven not heating to correct temperature almost always traces to one of four things: the temperature sensor, the bake element or igniter, the control board, or a thermometer reading taken at the wrong point in the cycle. That last one costs nothing to rule out, and it can make a healthy oven look broken. Most electronic controls also let you shift the oven’s reading yourself by up to about 19°C (35°F), with no service call. One warning before you start buying parts: an element that tests perfectly fine cold can still fail once there is heat in it.
The Temperature Sensor and the Numbers It Should Give
The sensor is the part most people replace first, and it is the only one in the oven you can check with a meter and a published number to compare against. It is a resistance probe. Resistance climbs as the cavity gets hotter, at something close to 2 ohms per °F, so the reading you take in a cool kitchen should sit a little below the room-temperature figure on the chart.
How it is metered:
- Run the oven until it has cycled on and off at least twice with the fault showing.
- Kill power at the breaker.
- Get to the control end of the sensor harness. The sensor leads are often violet.
- Unplug the sensor wiring.
- Meter across the two terminals in the connector block, on the 2k ohm range.
- Compare the result against the chart for your sensor type, allowing for the temperature of the room you are standing in.
Published charts for the common sensor put it at roughly 1080 ohms at 21°C (70°F), around 1143 ohms at 38°C (100°F), 1453 ohms at 121°C (250°F), 1654 ohms at 177°C (350°F) and 1852 ohms at 232°C (450°F), with tolerances in the range of 5 to 13 ohms. An 18°C (65°F) kitchen reads nearer 1060 than 1080.
How far off is too far is not firmly settled in published guidance. A reading a few tens of ohms out at room temperature is borderline; about 100 ohms out, roughly 10%, is where replacement gets recommended. There is nothing to adjust on the probe, so an out-of-spec sensor gets swapped.
One check before you condemn it. Not every oven uses the 1080 ohm type, and at least one variant should read only about 16 ohms at 21°C (70°F). A reading nowhere near the chart can mean you compared against the wrong spec rather than that the probe is dead. It is also worth looking at where the probe sits, since one resting against the cavity wall is not reading the air the food is in.
The Element on an Electric Oven and the Igniter on a Gas One
A good cold resistance reading on a bake element makes the element less likely. It does not clear it. Elements can fail with heat in them and test fine on the bench, and nobody has a trustworthy number for how often that happens. So a cold test that comes back clean narrows the field, it does not close it.
Gas is where the common mistake lives. The igniter and the oven safety valve are wired in series, and it is the igniter’s own current draw that pulls the bimetal valve open. A tired igniter can glow bright orange and still never draw enough to open the valve. “It glows, so the igniter is fine” is the most common misdiagnosis on a gas oven.
Same reason you cannot run a gas oven with electronic ignition off a match during a power cut, even though the cooktop burners light happily.
The test the service documentation specifies is current draw, not a stopwatch on the glow. It is taken with a clamp ammeter around one leg at the bimetal valve, power on, thermostat at 177°C (350°F), and the main or oven gas shut-off closed while the reading is taken. The figures depend on the igniter:
- Norton, flat or rectangular: 3.2 to 3.6 A
- Carborundum, round or cylindrical: 2.5 to 3.0 A
- The exception: a flat, Norton-shaped igniter with a powder-blue ceramic body is rated at 2.5 to 3.0 A, not the Norton figure. Robertshaw lists it as the 41-208 blue ceramic flat.
Each igniter needs the matching bimetal gas safety valve, so shape alone is not enough to tell you what the reading should be. An igniter pulling within spec while the valve stays shut points at the valve rather than the igniter.
That current test is done with the oven powered and gas isolated, which is why it belongs to a technician rather than to you.
When the Fault Sits in the Thermostat or Control Board
Some temperature faults never touch the sensor, and they tend to announce themselves differently.
On ovens with electronic controls, running hotter than the setpoint is often put down to a stuck bake relay rather than a drifting probe. Repeated arcing welds the relay contacts closed. After that the board cannot cut power to the bake element, whatever the sensor is telling it. Many ovens answer an overheat by shutting the oven down and throwing an error code, so a runaway control usually reports itself as a lockout rather than quietly baking hot.
The split is not as clean as hot equals board, cool equals sensor. A board fault can also starve the element. One documented case had an oven stalling at 160 to 166°C (320 to 330°F) against a 190°C (375°F) setpoint, with a bake relay showing excessive contact resistance and a sensor reading 14°C (25°F) high at the same time.
A failing board can also misread what the sensor sends it, or lose its stored calibration values. A faulty input circuit on the board can throw a sensor error code for a probe that is perfectly within spec. That is the argument for metering the sensor before you buy one: the code names a part, not a culprit.
What to Hand Over to a Technician
A smell of gas at the oven is not a diagnostic step. Shut the gas supply off if the valve is safely reachable, leave the house without touching electrical switches or lighting anything, and call your gas provider from outside.
The oven safety valve is replaced rather than repaired, and published guidance is uniform that the job belongs to a qualified technician. The risk is gas escaping from a connection that was not resealed properly.
The line for everything else runs roughly where live power starts. Metering the sensor happens with the breaker off, which is why it is reasonable to do yourself. The igniter current test happens with the oven powered up and the gas isolated, and sealed components are not homeowner work either.
Confirming the Oven Is Not Heating to the Correct Temperature
Before any of that, prove the oven is actually wrong. A cavity is designed to swing above and below the setpoint as the element or burner cycles, so a single thermometer reading captures a point on that swing rather than the oven’s working temperature.
Set it up this way. Oven thermometer on the centre rack, clear of both the lower and upper elements, nothing else in the cavity, and an easy-to-read setting such as 93°C (200°F) or 150°C (300°F).
Then leave it alone. Reading at the preheat beep catches the overshoot, not the steady state, so give it around ten minutes past the beep before you look. Opening the door even briefly pulls the cavity temperature down, so read through the glass where you can.
The size of the normal swing is not agreed on, but the pattern is: gas swings most, convection least, with electric overshooting after preheat. Figures in the range of 6 to 17°C (10 to 30°F) either side of the setting get quoted for gas. Which means an exact match between thermometer and display is not a standard any working oven can meet.
Take readings at more than one setting and over more than one cycle before you call it faulty.
The Calibration Offset and What Its Limit Tells You
If the oven really is out, the first fix is free and already built into the control. GE ovens let the set temperature be adjusted up to 35°F hotter or 35°F cooler, in 1°F increments, from the control panel.
Getting into the menu depends on the control. On GE models it is press and hold Bake and Broil for three seconds, with the display showing SF or OFFSET; or hold the + and – pads, with the display showing OFSt; or press Settings and choose option 5.
Two things catch people out. On keypad models the sign is set by pressing Bake again to toggle between positive and negative, which is how somebody enters 35 and ends up with an oven 19°C (35°F) further off in the wrong direction. And the offset applies to bake only. It does not change broil or self-clean temperatures, so an oven browning wrong under the broiler will not be corrected by calibrating bake. On a double oven, each cavity is calibrated separately with its own offset. The value stays in memory after a power failure.
The cap is the useful part. If you have spent the full 19°C (35°F) and the oven still bakes wrong, the offset is masking a fault rather than correcting one, and the sensor, the element or igniter, and the board are back on the list.
At that point, book a technician and have three things ready: your model number, whether the oven is gas or electric, and what the thermometer actually read at two different settings.
