How does a thermostat work?

A thermostat is a device connected to your central heating which allows you to control the heating in your house.

Most modern thermostats are digital however some older homes may still have the old style of thermostat which composes of a glass vial with a small amount of mercury inside. These older thermostats are known as mercury switches and are connected to three wires with one going across the bottom of the mercury, one to the left and the other to the right of the liquid metal.

This mercury switch is itself connected to a coil of two different metals laminated together which expand and contract as they heat up or cool down. As the coil unwinds, due to the different rates of expansion and contraction of the two metals, it tips the mercury either to the left or right, connecting it to the wire placed next to the metal.

These thermostats have two switches, one for heating up the metal coil, one for cooling it down. When activated these correspond to the way the mercury is tipped, either connecting to the wire that triggers the central heating system or the one that turns it down. When tipped neither way the circuit is broken and the heating turned off.

Digital thermostats use a far more simple method of heat control. These thermostats use a device called a thermistor to measure the temperature of your heating system. The thermistor is a resistor which allows electrical resistance changes that correspond to the temperature. The microcontroller in a digital thermostat measures the resistance and converts the number to a temperature reading.

Digital thermostats can also allow you to set the temperature in your home in a way older ones cannot. The temperature on a digital thermostat can be set precisely to the temperature you want and in return show you the current temperature in your house. You can also programme their settings to automatically turn up the heating or turn it down at certain points in the day and means you can have the heating turned down when you don’t need it saving you money on your heating bills.

A thermostat can also be found on your boiler. This thermostat presents itself as a dial or, on more modern boilers, a digital device similar to the conventional digital thermostat. The boiler thermostat sets the temperature of the water that is pumped through your radiators and the higher this is set, the quicker your home will be heated. When it is very cold outside you will need to keep this high as it will take longer for your home to heat up.