Thermostats and controls

The right heating controls will let you keep your home at a comfortable temperature without wasting fuel or heat.

If you have a central heating system, whether its gas, LPG or oil-fired, your full set of controls should ideally include a boiler thermostat, a timer or programmer, a room thermostat and thermostatic radiator valves (TRVs).

If you have an electric storage heating and hot water system, read our guide on electric heating systems for information about suitable controls.


What are the benefits of heating controls?

  • You’ll reduce your carbon dioxide emissions.
  • You’re likely to save money on your heating bills by installing and using your controls efficiently.

    Average savings for a typical three-bedroom semi-detached home, heated by gas:

    Action Potential savings per year 
    Installing and correctly using a room thermostat and thermostatic radiator valves £80 - £165 and 330kg - 680kg carbon dioxide                      
    Fitting a hot water tank insulation jacket £25 - £35 and 110kg - 140kg carbon dioxide 
    Turning room thermostat down by one degree £85 - £90 and 310kg - 360kg carbon dioxide 


  • You can schedule your heating and hot water to go on and off when needed.
  • You can select areas of your home to heat and the required temperature for each room, rather than heating a whole house at the same temperature.
You can upgrade or install heating controls without replacing your boiler, and it’s a particularly good idea to think about this if your controls are over 12 years old. Room thermostats, for example, are much more accurate now than they used to be.


Temperature controls

Room thermostats

These prevent your home from getting warmer than necessary. They turn the heating on until the room reaches the temperature you have set, and then off until the temperature drops.

Room thermostats need a free flow of air to sense the temperature, so they must not be blocked by curtains or furniture, or put near heat sources.

Your room thermostat should be set to the lowest comfortable temperature - typically between 18 and 21 degrees.

You don’t need to turn your thermostat up when it is colder outside; the house will heat up to the set temperature regardless. It may take a little longer on colder days, so you might want to set your heating to come on earlier in the winter.

A programmable room thermostat combines time and temperature controls and allows you to set different temperatures for different times of the day. You can have different temperatures in individual rooms by installing thermostatic radiator valves (TRVs) on individual radiators.

Thermostatic radiator valves (TRVs)

Thermostatic radiator valves do not control the boiler, they reduce the flow of water through the radiator which they are fitted to when the temperature goes above a certain setting. Set them to the level you want for the room; a lower setting uses less energy and so will save you money.

We do not recommend using radiator covers because TRVs sense the air temperature around them and control the flow rate depending on what level they're set at. Having a cover over the radiator means the TRV is enclosed, which is likely to make it think that the room temperature is higher than it actually is.

If you already have a radiator cover that cannot be removed, then it is still worth using TRVs to control the temperature as much as possible. If you feel the radiator is not hot enough at a particular setting, you can turn up the TRV.

Zone control

Save money by avoiding overheating parts of your home that are unoccupied or need lower temperatures, for example bedrooms or rooms with lots of glazing. You can have separate heating circuits with their own programmer and room thermostat (or programmable room thermostat) or set zones by using TRVs.

Cylinder thermostats

If your hot water is stored in a cylinder, the thermostat will prevent it becoming hotter than it needs to. Once the water has reached the temperature you have set, the heat supply from the boiler will be turned off.

Turning the thermostat higher will not make the water heat up any faster, and the water heating will not come on if a time switch or programmer has switched it off.

Cylinder thermostats are usually fitted between one quarter and one third of the way up the cylinder. They have temperature scales marked; you should set them at between 60 and 65 degrees. This is hot enough to kill harmful bacteria in the water, but it’s also hot enough to scald. For extra safety consider installing a thermostatic mixing valve which will automatically ensure that hot water is at a safe temperature.

Boiler interlock

This is not a control but a system of wiring that turns the boiler off when neither the room thermostat nor the cylinder thermostat needs it. Without this, the boiler can continue to ‘cycle’ and waste energy.

Boiler thermostat

Your boiler will usually have a dial on it, marked in numbers or from Min to Max. This sets the temperature of the water that will be pumped from the boiler through the radiators. The higher this is set, the quicker and more effectively the system will heat your home. In fact, if it is not set high enough, when it is very cold outside your home may not reach the desired temperature.

If you have a room thermostat and a boiler interlock, you can set the boiler thermostat quite high, letting the room controls do their job. But set it lower if there is anyone vulnerable in the household who might hurt themselves by coming into contact with very hot radiators or pipes.

Your boiler control thermostat should always be set to a higher temperature than the cylinder thermostat. In most boilers, a single boiler thermostat controls the temperature of water sent to both the cylinder and radiators.

Timing controls

Programmer or time control

This will automatically switch your heating off when you’re not at home, or when you don’t need it, such as when you’re in bed.

Programmers allow you to set ‘on’ and ‘off’ time periods. Most models will let you set the central heating and domestic hot water to go on and off at different times. There may also be manual overrides. Check that the timer on the programmer is correct before you set your programmes. You may also need to adjust it when the clocks change.

Choose a cold evening and time how long it takes for your house to warm up to a comfortable temperature – this is the warm-up time. Then turn the heating off completely and time how long it takes for the house to start to get uncomfortably cold – this is the cool-down time.

You can now set your timers including the warm up and cool down time. For example, you can make sure that the heating goes on with a warm-up time before you wake up and turns off before you leave the house. If you insulate your home, it will warm up faster and cool down more slowly, so you’ll save money on heating.

Set your water to heat up only when you need it. If your hot water cylinder or tank is well insulated, you may even find that the hot water supply in the morning stays hot enough to use in the evenings.