Central Heating Thermostats
A room thermostat switches the system on and off as necessary. It works by sensing the air temperature in the room - if it rises above the your chosen setting, for example 20°, then your heating system will be switched off (but not the hot water - it's controlled separately).
The room thermostat is best positioned in a living room, rather than the hallway, so it is not affected by the front door being opened.
Do not confuse the main room thermostat with TRV - thermostatic radiator valves.
You can buy programmable thermostats. This is combined time switch and room thermostat that allows the user to set different periods with different target temperatures for space heating.
Thermostatic radiator control valves (TRVs)
These switch individual radiators on or off, depending on the warmth of each room. They usually have a numbered wheel marked with a * and numbers from 1 to 5. The * setting is to protect against frost; it will usually leave the radiator switched off unless the temperature falls below 6°C or so. For a lounge or living room a setting of 3 or 4 is usually sufficient; a bedroom might be 1 or 2. A wax filling in the head of the valve operates valves and shuts off the radiator when it reaches specific temperatures.
Generally, one radiator should not be fitted with a Thermostatic radiator control valve, unless the boiler is fitted with a flow meter to detect when all Thermostatic radiator control valve are closed. This radiator may be a bathroom towel rail, or in the same room as the room thermostat. It is not a good idea to have a Thermostatic radiator control valve on the radiator in the same room as the main thermostat, because if it turns the radiator off, the low temperature in the room can mislead the main thermostat into thinking the whole house is cool. In the same way, if there is a fire in the same room as the thermostat the heat from the fire may fool the thermostat into switching off the heating. Modern Thermostatic radiator control valves are dual flow - they can be fitted on the flow or the return - older ones were designed to be fitted on the flow - ie the hot water going into the radiator.
Thermostatic controls on the hot water system
These are attached to the hot water cylinder and control the temperature of the water in the cylinder. When the water temperature reaches the set level - usually about 60° the three port valve stops the flow of hot water to the cylinder.
The room or space thermostat and the hot water thermostat should be connect/ wired to the boiler.
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