In home central heating there are three main groups, Temperature, Time and Heated water Distribution.
In Home Central Heating Thermostats are used to control temperature. A Thermostat senses the change in temperature and then Open or Close electrical circuits as required, in response to the change.
The Boiler thermostat controls the temperature of the water in the Boiler. If it is set to 80°C then when the water temperature reached, the thermostat will cut off power the gas valve and turn off the burners.
The Room thermostat or Room stat is used to detect changes in the temperature of the air in the room. If the required temperature of the room stat is set to 20°C then when the room's air temperature reached the set value the room stat will turn off power to the boiler and pump. This way it will maintain the comfort level and also note it stops the boiler burning gas, hence reduce the gas bill.
Cylinder thermostat or cylinder stat is fitted on to the hot water cylinder to sense the temperature of the hot water. When the set temperature is reached, depending on the system design the cylinder stat will divert the hot water from the boiler or turn off boiler and pump.
A Frost thermostat or Frost stat is in fact a room stat with the required temperature set at value 5°C and wired such a way the it can turn on the central heating by switching on the boiler and pump even the central heating system is switched off. Hence save the boiler and pipe work from frost damage.
A thermostatic radiator valve is fitted on a radiator in place of the hand control. It has a temperature sensor built-in to the valve. When the room temperature reaches the set value on the valve, it mechanically closes valve.
The purpose of the time control is to switch ON and OFF central heating when it is required. Thus reducing the running cost of the central heating system and gas bill.
These are simple power ON/OFF devices. They can switch the central heating ON and OFF once, twice even many times.
We may not want heating at the same time as the hot water. A programmer can turn on/off hot water and central heating separately.
We require the Central Heating System to provide heating for different zones or areas (for example first floor and ground floor) at different times or at different temperatures from each other, this is accomplished by fitting distribution controls.
Zone Valve consist of a electric motorised valve and a spring. When the valve is powered the valve open and the power is off the spring closes the valve.
For example we may want the bed rooms only heated an hour before we get up and then again an hour before going to bed. This can be achieved by having Zone valves on the bed rooms pipe work connected to a timer switch.
A diverter valve can divert the heated water from the boiler into two circuits/pipe works or zones. Usually between hot water circuit and central heating circuit.
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