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How do room thermostats work?
Attached to the hall, or living room wall, the thermostat is often an overlooked piece of equipment and after the boiler, it has the most to do with your house heating.
Firstly though, make sure the boiler thermostat is set properly, as this is the best starting point for getting the most from your central heating system. Most have two settings, Summer and Winter, so ensure that your setting matches the right time of year.
Secondly, the traditional home thermostat is made up of a mercury switch, thermometer coils and a heat anticipator.
Taking these components in order, the mercury switch is a key player. It is a glass vial containing mercury. As a reminder, mercury, a liquid metal, flows like water and conducts electricity. In a typical heating thermostat, the mercury vial would have three wires inside, one on the left, one on the right and one along the bottom. The vial tips left, the left and bottom wire make contact; the vial tips right, and the right wire and bottom wire make contact. Simple really.
Next the thermometers – usually two (controlling say water temperature and central heating temperature) – which are basic coiled bimetallic strips. Right, the principle here is that the metal coils of the two thermometers expand and contract at set rates as they heat, or cool down. The coil’s centre is attached to the temperature control switch and the end is attached to the mercury vial.
Okay so far? Right, lets say you turn up the temperature control on your thermostat. This in turn rotates the coil of metal and tips the mercury switch to the left. As the left and bottom wire connect (remember those?), a circuit is created and a relay is energised which signals the boiler to turn on. As the heat from the boiler does its job via the radiators, the coil of wire contracts at the set rate and the vial is tipped to the right, cutting the circuit and turning the heat off.
Eventually the heat will reduce once the boiler has switched off the heat source diminishes and the coil expands again to the level set previously, and on comes the heating again.
Very clever, but quite simple really. Of course, that’s just the inner workings, there might be a number of other buttons and knobs, but the basic thermostat is just there to allow you some degree of temperature control.
And that is why, if you think about it, it’s vital that that you have it sited in the best possible place in the house, as icy draughts, cold rooms, or sunny rays can all distort its operational dynamics.
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