How To Test An Oven Temperature Control Thermostat

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Have you been finding those homemade muffins you like to have for a weekend breakfast are taking a lot longer to bake than they used to? Maybe it’s been a while since you’ve cleaned the oven, so you select the self-cleaning function only to discover that function doesn’t seem to work. Or, perhaps, the oven just isn’t heating up at all. All of these problems could be caused by a faulty oven temperature control thermostat. In this article, Repair Clinic will discuss the differences between an oven control using a control board and sensor and one that uses a temperature control thermostat assembly, plus an effective way to determine if the thermostat assembly is working properly or not.

Two kinds of oven controls

Whether you rely on a gas or electric range/oven to prepare your meals, the appliance will have one of two different kinds of oven controls. Most modern models will use an electronic control board that works with an oven sensor to set and monitor the oven’s temperature, while older or less expensive models will use a switch-based thermostat and sensing bulb assembly to set and monitor the temperature.

How the oven control works

On ovens that use an electronic control board and temperature sensor, the user will press a button on the control panel to select an appropriate oven temperature. The appliance’s control will utilize the sensor to assist in regulating the oven temperature by monitoring the resistance to the electrical current as the temperature varies. For ovens that use a temperature control thermostat, the user will rotate a dial to select an oven temperature. The thermostat’s sensing bulb contains a liquid that expands when heated and contracts when cooling down. This signals a capillary system to cycle the control on and off to regulate the oven temperature. When the selected temperature is reached, the control will then shut off the voltage to the igniter (gas ovens) or to the heating element (electric ovens). This cycle is repeated throughout the baking or broiling process to maintain the proper oven temperature.

Actual oven temperature will fluctuate throughout the baking/broiling cycle

The temperature designated by the control is only an average; the actual temperature will fluctuate throughout the baking or broiling cycle. Convection ovens will reduce this fluctuation by using a motorized fan, with or without its own heating element, to circulate the heated air evenly throughout the oven cavity.

A defective temperature sensor/thermostat will result in inaccurate heating

So what happens if a temperature sensor or thermostat fails? The simple answer is the oven may not heat up accurately. This can mean the oven may only heat up to 200° Fahrenheit when you’ve selected a cooking temperature of 350° Fahrenheit. It can also mean the oven could heat to a temperature much higher than the one selected, or be unable to enter a self-cleaning cycle, or it might not be able to heat at all.

Testing an oven temperature control thermostat

Since a faulty oven sensor or thermostat isn’t the only cause of incorrect oven temperature, it is recommended you test the component with a multimeter to help determine if the part is functioning appropriately or not. While oven sensor testing is relatively straightforward, testing an oven temperature control thermostat will involve an electric griddle or another heat source.

The first step is to uninstall the temperature control thermostat assembly

For proper testing, the first step is to fully uninstall the temperature control thermostat assembly from the appliance. Before you begin any disassembly to reach the thermostat, be sure to unplug the appliance’s power cord or shut off the power supply. On oven models that use a thermostat, the component is located in the control housing directly behind the control panel dial that you use to select the oven temperature. You will need to pull off the dial itself then remove the control housing’s rear access panel. Disconnect the wires from the thermostat and unthread the mounting screws to release the component from the control panel. The thermostat will have a long wire that leads to a sensing bulb that can usually be found secured near the top of the oven cavity. Detach the sensing bulb and fully remove the whole thermostat assembly.

Identify the correct thermostat terminals for testing

You’re going to be using the multimeter to test for an interruption in electrical continuity – a continuous electrical path present in the component – as the thermostat’s sensing bulb heats up. Continuity tests are performed by contacting the meter leads to a component’s power input and output terminals. Since a temperature control thermostat can have more than two terminals, you may need to refer to the oven’s wiring diagram to identify the component’s primary cycling terminals.

Testing for an interruption in electrical continuity

Here are the seven steps to test a temperature control thermostat assembly:

  1. Rotate the range selection dial on the multimeter to the lowest setting for ohms of resistance.
  2. Confirm the thermostat dial is turned to the “on” position at a low to medium temperature setting. If you noted the position of the thermostat when it was still installed in the control housing, you can replace the dial on the switch stem to better understand what temperature setting you’re selecting. Otherwise, it’s okay to use some guesswork.
  3. Contact the black meter lead to one of the thermostat’s primary terminals and the red lead to the other primary terminal.
  4. Check the meter display to see if it shows close to zero ohms of resistance. If it does, you’ll know the thermostat has continuity at room temperature which means the component is functional… so far.
  5. For the next part of the test, place the thermostat’s sensing bulb on the surface of the electric griddle (you may need to weigh it down with a small metal object such as a socket).
  6. Set the griddle to a temperature higher than what you suspect the thermostat is set at.
  7. Observe the multimeter display for a change in the ohms of resistance. As the sensing bulb heats up, the contacts in the thermostat should open and interrupt the continuity (no ohms of resistance). If this happens, the thermostat assembly should be fully functional. However, if the meter display continues to show close to zero ohms of resistance, then the thermostat’s contacts have remained closed and the thermostat is not responding correctly to temperature changes. Of course, if the thermostat won’t respond to a change in temperature, you’ll know the part is defective and will need to be replaced with a new one.
Oven Temperature Control Thermostat Testing

Oven repair resources are available from Repair Clinic

Repair Clinic provides model-specific procedural videos and step-by-step guides to assist you with your oven repair, whether you need to install a new temperature control thermostat, replace a heating element, or change out a door switch. Enter the full model number of your range or oven in the “Videos & Articles” search bar to see all the free resources available to you.

Find genuine OEM oven parts with Repair Clinic

As your repair partner, Repair Clinic knows that fixing it right means using a genuine manufacturer part, not just a generic one. You can find the exact genuine OEM oven part you’re looking for by entering the full model number of the GE, Bosch, KitchenAid, Electrolux, LG, Kenmore, Samsung, Hotpoint, or whatever other brand name range/oven you need to repair, into the Repair Clinic “Shop Parts” search bar. The resulting comprehensive part list can then be narrowed down by using the “Part Category” and “Part Title” navigation filters.

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