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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.

The newest technology: smart heating controls

Smart heating controls on a phone

Several companies offer more advanced control systems for domestic central heating, generally known as smart heating controls. They allow you to manage your heating controls remotely from a computer, tablet or smart phone, and many incorporate other advanced features to control your heating in more sophisticated way. Some can learn from your previous choices and make adjustments for you, while others use automation and optimisation features to help determine exactly when to turn the heating on. One clear advantage of a smart heating control system is
that you can make changes remotely if your plans change – for example, you can change the time that your heating comes on if it turns out you will be home sooner or later than you thought.

Whether a smart controller will save you money, and whether it is right for you, will depend on your lifestyle, how you currently control your heating and whether you prefer using an app to using a traditional controller.

What are the benefits of heating controls?

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

Action

Potential savings per year 

Installing and correctly using a programmer, room thermostat and thermostatic radiator valves £75 and 340kg carbon dioxide                      
Turning room thermostat down by one degree £80 and 350kg carbon dioxide 

Typical savings for a typical three-bedroom semi-detached home, heated by gas. Figures are based on fuel prices as of April 2017.

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 14 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.

Hot water 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.

If you have a combi boiler then you won’t have a cylinder, but there will probably be a hot water thermostat on the boiler itself. This is often a dial with a picture of a tap on it.

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 it 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. However, condensing boilers work more efficiently when the water returning to the boiler is below 55 degrees, so it can be better not to set the temperature too high.

If you have a regular boiler with separate hot water cylinder, your boiler thermostat should always be set to a higher temperature than the cylinder thermostat, otherwise the hot water cylinder will never get up to temperature. If you have a combi boiler you will probably have two dials – the one with a radiator symbol controls the output to the radiators and you can set this at the best point for your heating without it affecting the hot water temperature.

Automatic boiler thermostats

Weather compensation

When the weather is cold you need your boiler stat to be set to a high level to make sure your house can get warm enough. If the weather is milder you could turn the boiler stat down and still be warm enough. This will make the system more efficient, especially if you have a condensing boiler. A weather compensator does this for you automatically by measuring the outside temperature and adjusting the boiler thermostat temperature as required.

Load compensation

When your heating first comes on the house may be very cold, especially when the weather is cold. You will want your boiler stat to be set high so that your house can heat up reasonably quickly. But if the house is fairly warm and you only need to raise it by a couple of degrees, you could risk overheating the house by heating the radiators up to full, which will then continue heating the house after it has reached the temperature you want. A load compensator measures the difference between the internal temperature and the set temperature of the thermostat, and adjusts the boiler thermostat as appropriate to avoid overheating. 

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 and hold the heat more efficiently, 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.

Zone control

Most households want to heat different rooms at different times of the day. You can do this by turning individual radiators on and off at different times, but lots of people don’t get round to these.

Zone control does this for you automatically by having separate heating circuits for different parts of the house, with a separate programmer for each circuit. If you’re fitting a new heating system, then you may want to consider zone control to help you keep heating costs down. And if you’re fitting it in a large house, you may be required to have two separate zones to meet the regulations.

If you’re not fitting a new system, it may be impractical to convert your existing pipework. In this case you want to consider programmable TRVs.

Programmable TRVs

These are temperature controls for individual radiatiors, just like standard TRVs, but with timing control as well. So you can set each radiator to come on at different times, and heat each room only when you want to.

Optimisation

An optimiser works out how long it takes your house to heat up, and turns the heating on at the right time so your house will be up to temperature just in time for when you need it. For example, if you get up at 7:30 in the morning you can set your programmer to 7:30am, and your thermostat to whatever you choose, and the optimiser will work out when to fire up the boiler so the house is up to the temperature you set by 7:30am. In colder weather, it will fire up earlier and in milder weather it will wait a bit, saving you energy and money.

Optimisation is one of a number of features that may be available if you fit a smart heating control system.

Automation

An automated heating control system works out whether and when to turn the heating on based on whether there is anyone in the building, or whether you are approaching the building. It may use sensors in the home or it may track your phone’s location to decide when to turn the heating on. Automation is available as part of some smart heating controls, and generally includes an optimisation function to help decide when to turn the heating on.

More information

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If you're based in England or Wales, contact the Energy Saving Advice Service on 0300 123 1234 from Monday to Friday, between 9am to 8pm. (Calls cost no more than national rate.)

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