Cooker oven thermostats - operation, testing and common issues

The thermostat is very important part of an oven as they regulate the temperature inside the ovens cavity. The thermostat is part of the heat selector switch and detects heat within the cavity by means of a capillary tube.

When the oven heats up the gases inside the capillary tube expand this puts pressure on an electrical contact inside the thermostat as the heat rises eventually the expansion of these gases will open the electrical contacts turning off power to the heating element, the cavity will them begin to cool again and the gases in the capillary tube will contract again until the electrical contact makes contact again and turns the element back on. This cycling on and of of the element is what keeps the oven at the desired temperature.

The electrical connection point can be varied by adjusting the selector switch, if you select a higher heat setting then it will take longer for the expansion of the capillary gases to disconnect the element this means an higher temperature will be achieved as the element is kept on for longer. This allows some control of the temperature inside the oven to control if the cooking.

Buy cooker oven spares on Ebay UK here 

Buy a good Multimeter on Ebay UK here 

Buy a good Multimeter here 

Common issues 

Over time the thermostat can go out of tolerance so the temperature setting is different to the actual cavity temperature you can test this by measuring the temperature inside the cooker. This has do be done over a certain period of time usually over 4 heat cycles of the thermostat to ensure the thermostat is regulating temperature correctly and the temperature of the oven is stable. 

So set temperature meter up to take the oven temperature and watch the thermostat light go on and of 4 times while monitoring the temperature, if this is out by 10% of the selector temperature then the thermostat needs replacing ( Central oven temp test ).

When cold or at room temperature with the selector switch on the thermostat should have continuity and when off it will read open circuit see video below on how to do this in more detail.

Testing the thermostat for continuity room temperature ( video )

Central oven temperature testing