Here is guide to what heating controls you should have and what they do, text courtesy of TACMA:

Recommended Minimum Standards

The recommended minimum standard for controls is that they should perform the following functions:

Automatically turn off heating when not required

This is usually referred to as ‘time control’ and generally requires a programmer to switch your heating off when you’re not at home, or when you can do without it, such as when you’re in bed.

Automatically prevent the building getting warmer than it needs to be.

This is usually referred to as ‘temperature control’ and generally requires a room thermostat. This should allow you to set a comfortable temperature for your home and it will then automatically turn the heating off when that temperature is achieved. The heating will therefore only come on to maintain the comfort temperature that you require. A programmable room thermostat will combine time and temperature control and allows you to set different temperatures for different times of the day.

Avoid overheating parts of the house that are unoccupied or need lower temperatures

This is referred to as zone control. Separate zones are usually set to provide lower temperatures in bedrooms but can also be used to take advantage of ‘passive solar gains’ in rooms with lots of glazing, or to flexibly accommodate specific usage patterns such as a home office or granny flat. Zones are often provided through the application of thermostatic radiator valves, but can also be done with separate heating circuits each with their own programmer and room thermostat (or programmable room thermostat.)

Prevent stored hot water being hotter than it needs to be

If your hot water comes from a storage cylinder then you should have cylinder thermostat. This allows you to set a maximum temperature for the stored hot water and will then automatically stop the water being heated once this temperature is reached. There are two further elements of the controls system that you need to be aware of:

Boiler interlock This is not a control but a term for the system of wiring that turns the boiler off when neither the room thermostat nor the cylinder thermostat is calling for heating. Without this the boiler can continue to ‘cycle’ (i.e. to use energy) even though none of this energy provides any benefit to you. So a boiler interlock is an important way of making sure that your system is energy efficient.

Boiler thermostat Your boiler will usually have a dial type control on it, marked something like ‘Min’ to ‘Max.’ This sets the temperature of the water from the boiler, which will then go through the radiators to heat your home. The higher this is set, the quicker and more effectively the system will heat your home. In fact, if this is not set high enough when the outside temperature is very cold then your home may never reach your desired temperature.

As long as you have a room thermostat and a boiler interlock then it is reasonable to set the boiler thermostat on a high level, letting the room controls do their job. (Note: If there are vulnerable people in the household you may wish to avoid situations where they could come into contact with very hot radiators or pipework – it is best to seek expert advice on this).

What is a programmer?
Programmers allow you to set ‘On’ and ‘Off’ time periods. Some models switch the central heating and domestic hot water on and off at the same time, while others allow the domestic hot water and heating to come on and go off at different times.

Set the ‘On’ and ‘Off’ time periods to suit your own lifestyle. On some programmers you must also set whether you want the heating and hot water to run continuously, run under the chosen ‘On’ and ‘Off’ heating periods, or be permanently off.

The time on the programmer must be correct. Some types have to be adjusted in spring and autumn at the changes between Greenwich Mean Time and British Summer Time. You may be able to temporarily adjust the heating programme, for example, ‘Override’, ‘Advance’ or ‘Boost’.

These are explained in the manufacturer’s instructions. The heating will not work if the room thermostat has switched the heating off. And, if you have a hot-water cylinder, the water heating will not work if the cylinder thermostat detects that the hot water has reached the correct temperature.

What is a room thermostat?
A room thermostat simply switches the heating system on and off as necessary. It works by sensing the air temperature, switching on the heating when the air temperature falls below the thermostat setting, and switching it off once this set temperature has been reached.

Turning a room thermostat to a higher setting will not make the room heat up any faster. How quickly the room heats up depends on the design of the heating system, for example, the size of boiler and radiators.

Neither does the setting affect how quickly the room cools down. Turning a room thermostat to a lower setting will result in the room being controlled at a lower temperature, and saves energy. The heating system will not work if a time switch or programmer has switched it off. The way to set and use your room thermostat is to find the lowest temperature setting that you are comfortable with, and then leave it alone to do its job.

The best way to do this is to set the room thermostat to a low temperature – say 18°C – and then turn it up by one degree each day until you are comfortable with the temperature. You won’t have to adjust the thermostat further. Any adjustment above this setting will waste energy and cost you more money. If your heating system is a boiler with radiators, there will usually be only one room thermostat to control the whole house. But you can have different temperatures in individual rooms by installing thermostatic radiator valves (TRVs) on individual radiators.

If you don’t have TRVs, you should choose a temperature that is reasonable for the whole house. If you do have TRVs, you can choose a slightly higher setting to make sure that even the coldest room is comfortable, then prevent any overheating in other rooms by adjusting the TRVs. Room thermostats need a free flow of air to sense the temperature, so they must not be covered by curtains or blocked by furniture. Nearby electric fires, televisions, wall or table lamps may prevent the thermostat from working properly.

What is a programmable room thermostat?

A programmable room thermostat is both a programmer and a room thermostat. A programmer allows you to set ‘On’ and ‘Off’ time periods to suit your own lifestyle. A room thermostat works by sensing the air temperature, switching on the heating when the air temperature falls below the thermostat setting, and switching it off once this set temperature has been reached.

So, a programmable room thermostat lets you choose what times you want the heating to be on, and what temperature it should reach while it is on. It will allow you to select different temperatures in your home at different times of the day (and days of the week) to meet your particular needs.

Turning a programmable room thermostat to a higher setting will not make the room heat up any faster. How quickly the room heats up depends on the design of the heating system, for example, the size of boiler and radiators. Neither does the setting affect how quickly the room cools down.

Turning a programmable room thermostat to a lower setting will result in the room being controlled at a lower temperature, and saves energy. The way to set and use your programmable room thermostat is to find the lowest temperature settings that you are comfortable with at the different times you have chosen, and then leave it alone to do its job.

The best way to do this is to set low temperatures first, say 18oC, and then turn them up by one degree each day until you are comfortable with the temperatures. You won’t have to adjust the thermostat further. Any adjustments above these settings will waste energy and cost you more money. If your heating system is a boiler with radiators, there will usually be only one programmable room thermostat to control the whole house. But you can have different temperatures in individual rooms by installing thermostatic radiator valves (TRVs) on individual radiators.

If you don’t have TRVs, you should choose a temperature that is reasonable for the whole house. If you do have TRVs, you can choose a slightly higher setting to make sure that even the coldest room is comfortable, then prevent any overheating in other rooms by adjusting the TRVs. The time on the programmer must be correct. Some types have to be adjusted in spring and autumn at the changes between Greenwich Mean Time and British Summer Time. You may be able to temporarily adjust the heating programme, for example, ‘Override’, ‘Advance’ or ‘Boost’.

These are explained in the manufacturer’s instructions. Programmable room thermostats need a free flow of air to sense the temperature, so they must not be covered by curtains or blocked by furniture. Nearby electric fires, televisions, wall or table lamps may prevent the thermostat from working properly.

What is a thermostatic radiator valve?
TRVs sense the air temperature around them and regulate the flow of water through the radiator which they are fitted to. They do not control the boiler. They should be set at a level that gives you the room temperature you want. These settings may have to be different in each room, and you should set the TRVs to suit each room and then leave them to do their job.

Turning a TRV to a higher setting will not make the room heat up any faster. How quickly the room heats up depends on the boiler size and setting, and the radiator size. Turning a TRV to a lower setting will result in the room being controlled at a lower temperature, and saves energy. TRVs need a free flow of air to sense the temperature, so they must not be covered by curtains or blocked by furniture.

TRVs cannot turn off the boiler when the whole house is warm. To do that, you will need a room thermostat as well. The radiator in the room with the room thermostat should not normally have a TRV, but, if it does, keep the TRV on the maximum setting and adjust the room thermostat as explained with the instructions.What is a cylinder thermostat?A cylinder thermostat switches on and off the heat supply from the boiler to the hot-water cylinder.

It works by sensing the temperature of the water inside the cylinder, switching on the water heating when the temperature falls below the thermostat setting, and switching it off once this set temperature has been reached.Turning a cylinder thermostat to a higher setting will not make the water heat up any faster. How quickly the water heats up depends on the design of the heating system, for example, the size of boiler and the heat exchanger inside the cylinder.

The water heating will not work if a time switch or programmer has switched it off. And the cylinder thermostat will not always switch the boiler off, because the boiler sometimes still needs to heat the radiators. Cylinder thermostats are usually fitted between one quarter and one third of the way up the cylinder. The cylinder thermostat will have a temperature scale marked on it, and it should be set at between 60ºC and 65ºC, then left to do its job.

The temperature needs to be this high to kill off harmful bacteria in the water, but you should note that this is still a scalding temperature and the hot water should be mixed with cold water for safe bathing, washing etc. For extra safety consider installing a thermostatic mixing valve which will automatically ensure that hot water is at a safe temperature.

If you have a boiler control thermostat, it should always be set to a higher temperature than that of the cylinder thermostat. In most boilers, a single boiler thermostat controls the temperature of water sent to both the cylinder and radiators, although in some there are two separate boiler thermostats.