Temperature errors fall into two categories - those that are only off slightly (perhaps 35 °F) and those that are off a great deal. For instance, at a setting of 350 °F, there may only be a very small amount of heat or a whopping 500 °F. Such extremes usually require a new thermostat. Thermostat replacement is a difficult task. (Refer to Manual 11: Ranges, Cooktops, and Ovens.)

Easy Calibration Problems

1. In a few situations, particularly modern designs, it is easy to calibrate an oven. The easiest of all is one with an adjustable thermostat knob. Remove the knob and check the reverse side for an adjustment. Calibrate with an oven thermometer over a period of at least 20 minutes. It is normal for an oven to fluctuate 25 °F above and below the set point. Aim for the average temperature.

2. A few are calibrated by a very tiny adjustment screw deep in the center of the thermostat shaft.

3. The adjustment screw on the majority of thermostats is accessed through a hole in the mounting flange or it is hidden by the mounting flange. It may be necessary to loosen the mounting to get to the adjustment.

Unfortunately, except on a oven less than a few years old, calibration seldom works. Only a novice will attempt calibration on an old oven. Once an oven begins to drift off temperature, it will continue to drift after calibration. A relatively new one may have been set improperly at the factory and need a one time adjustment. In general, a new thermostat is the only reliable solution to incorrect temperatures.

There are a few exceptions to this rule. They are ovens that utilize 15 ohm sensor systems such as GE self-cleaning and new electronic (ERC) systems - (touch pad control designs). These two designs sense heat with an electronic device different from conventional capillary tubes and are repaired differently. Neither design has a conventional thermostat. (For complete details, see Manual 11: Ranges Oven and Cooktops.)

Difficult Calibration Problems

For a detailed analysis and repair of 15 ohm systems, ERC type systems and replacement of gas and electric thermostats see Manual 11: Ranges, Cooktops, and Ovens.