Thermostats are intended for switching electric circuits with respect to the temperature measured, in heating applications they typically switch on/off a heat source, maintaining a preset temperature. Thermostats are designed for panel mount (e.g. in a boiler), then their adjustable knob or reset pushbutton is placed on the panel, or for a free installation where the thermostat is placed inside a plastic box that ensures electric protection.

Operating thermostats switch a heat source directly, depending on the temperature set by a knob/screwdriver or at a fixed temperature.

Safety thermostats act as a kind of fuse when the operating thermostat fails. When the threshold temperature is exceeded, the thermostat opens its contacts. As soon as the temperature sinks, the contacts will either close again (in models with an automatic reset) or remain open and the appliance needs to be switched on by pressing a reset pushbutton on the thermostat (in the usually used models with a manual reset).