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Boiler controls and thermostats

By Matthew Knight

Find out how to use heating controls and thermostats to save money on your heating bills. 

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Having your heating at the right temperature will not only keep you cosy, but can also cut your energy bills. Use our expert tips to stay warm and save money.

One in four of you* have told us that you believe that the most efficient and cost-effective method of heating your home is simply leaving the heating on and setting the thermostat to a consistent temperature. This is definitely not the case. 

Effective heating controls are a vital part of an efficient boiler-powered central-heating system. Clever use of controls can help you minimise energy consumption by ensuring each room is at the right temperature for comfort, while avoiding overheating. This will keep your home cosy and cut your energy bills.

Keep reading for all you need to know about the different types of heating controls, and follow our quick and easy tips to help keep your energy bills, and your heating, under control.

Will your boiler let you down this winter? Our unique research reveals the most reliable boiler brands.

Top tips for using boiler controls and thermostats 

Room thermostats

A room thermostat works by sensing the air temperature in the room. It switches on the heating when this falls below the thermostat setting, and switches it off when the required temperature is reached. 

Because of this:

  • Your room thermostat should be positioned away from your boiler.
  • It will need a free flow of air to sense the temperature, so make sure yours isn't covered by curtains or blocked by furniture.
  • It should be set away from electric fires, TVs, walls or table lamps, as these may stop the thermostat from working properly.

Most heating systems have one thermostat, adjusting the temperature of the whole home based on the temperature of the room it's in. If this is the case for your home, it's best to locate it in the room you want to be warmest, such as the living room or bathroom.

Mechanical boiler timers

A simple mechanical timer usually gives you three options for running a central heating system: 

  • the boiler is off
  • the boiler is providing heat
  • the boiler turns on and off at set times.

Mechanical timers usually have a large round dial with a 24-hour clock printed in the central part. You turn the dial until it is set to the correct time and then leave it to switch on and off.

The outer portion of the dial consists of tabs, each representing a 15-minute period, that are pushed in to select when you want the boiler to turn on. 

This doesn't affect the temperature the boiler is set at. For that you will need a temperature control on your boiler, or a thermostat. 

Mechanical timers are simple to set, but your boiler always turns on and off at the same time each day. This may not suit you if you have different weekday and weekend routines. If you want flexibility, it's worth thinking about getting a programmer - see below.

The most efficient systems will allow you to have zoned heating, so you can set different temperatures in different rooms. One way of doing this is through a smart thermostat system, which will also allow you to control your heating from your phone when you're away from home.  

Get zoned heating for the most efficient system

Temperature tips:

  • Setting your thermostat to 19°C or 20°C is usually adequate 
  • Recommended night-time temperature is 16-19°C
  • Turning down your thermostat by just 1°C can save you £80 to £85 a year, according to the Energy Saving Trust.

But it's worth keeping in mind that babies should sleep in a room with a temperature between 16°C and 20°C, according to the Lullaby Trust. For older people and those with impaired mobility, Age UK says that the main living room temperature should be around 21°C, and the rest of the house at a minimum of 18°C.

Timers and programmers 

A timer lets you choose what times you want the heating to be on, and what temperature it should reach while it's on. These are also sometimes called one-day programmers or one-day programmable room thermostats - see an example of one below.

A seven-day programmer or programmable room thermostat makes it possible to set a different heating pattern for weekdays and weekends. Some timers allow different patterns for each day of the week - this can be useful if you work part-time or on shifts.

You can also get timers and programmers without thermostats, so you can set times your heating should be on, but not the temperature it needs to be at. 

Some timers and programmers are wireless, while others need to be wired to your boiler. 

As with room thermostats, timers and programmers with a thermostat need a free flow of air to sense the temperature, so they must not be covered. They should also be set away from sources of heat or cooling appliances. 

The time on a timer or programmer must be correct. Some types have to be adjusted when the clocks change to and from British Summer Time, while others will change automatically.

The time on a timer or programmer must be correct and it must have a free flow of air around it

If your heating system is a boiler with radiators, there will usually be only one programmable room thermostat to control your whole home. 

You can get models that allow you to program each room of your house differently, such as by using smart thermostat controls.

With some programmers and timers you can temporarily adjust the heating program. Common options are: 

  • 'Party' which turns the heating on for a few hours.
  • 'Override' lets you temporarily change the pre-programmed temperature during one of the programmed periods.
  • 'Holiday' turns the heating off for a set number of days.

Save money with the best heating controls and systems

Out-of-date central heating system components and controls can lead to wasted energy, costing you money. They can also create potential heating problems, which could mean forking out for expensive boiler repairs. 

Learn more about what you heating system includes, or lacks, below.

Gravity-fed hot water cylinder

Gravity-fed hot water cylinders work with heat-only boilers. With these systems, cold water is stored in a cylinder or tank at a high level in your home. It is then funnelled down when needed, using gravity, to a hot water cylinder below. From there, it is heated before being pushed out to your taps, radiators or shower. Systems with gravity-fed hot water cylinders are also known as low-pressure systems.

Why will this cost me money? Cold water that's stored is slow to reheat, which means you'll use more energy getting it up to the right temperature. 

How will I know if I have this? If you have a gravity-fed hot water cylinder, you'll usually have a tank in the loft, and another below it somewhere else in your home, often in the airing cupboard.

No cylinder insulation

Cylinders that are insulated have an extra layer of material so that heat is kept within the cylinder.

Why will this cost me money? If a cylinder is not insulated, heat will be wasted through its surface.

How will I know if I don't have this? Some cylinders have a layer of insulation on the inside, so you won't be able to see it from the outside. With others, they have what's called a 'cylinder jacket' wrapped around them, which acts as insulation. These are fully visible. If yours doesn't have one, you can buy one. 

No thermostatic radiator valves (TRVs)

Thermostatic radiator valves let you regulate the temperature of each radiator in your home that has one.

Why will this cost me money? If a radiator doesn't have one, when the heating is on it will heat the room to a hotter temperature than is needed.

How will I know if I don't have this? These are located at the end of a radiator, either at the top or bottom, attached to the pipe that runs from the radiator. Take a look at the image below to see what they look like.

No boiler interlock

A boiler interlock is an arrangement of wires that stops the boiler from producing heat when it's not needed. 

Why will this cost me money? This means the boiler stays hot unnecessarily, or keeps turning itself on and off, using more energy.

How will I know if I don't have this? It's usually present if you have a boiler thermostat, so if you have one of those, you'll have a boiler interlock. If you don't, take a look at the manual, or contact the manufacturer to find out.

No hot water cylinder thermostat

A thermostat does the job of keeping the water in your cylinder at a certain temperature. It does this by heating up the water if it goes below the stated temperature on the thermostat, and turning the heating within the cylinder off to stop it getting too hot.  

Why will this cost me money? If you don't have one, stored water can become too hot, using more energy than is necessary to heat it. It also means there is a risk of water scalding you. 

How will I know if I don't have this? Thermostats are small dials that have a range of temperature options around a central circle, as in the image below. If your cylinder has one, you'll be able to see it on the outside, around one third of the way up. 

No room thermostat

Like the thermostat on a cylinder, you can also have a thermostat in one room or each room of your house. Older versions are connected by wires running to your boiler, while newer systems tend to send signals to the boiler wirelessly.

Why will this cost me money? If you don't have a thermostat, it means rooms can be too hot, wasting energy and money, or too cold.

How will I know if I don't have this? If you have one, you'll be able to see a dial on the wall. Take a look at the image above to see what one looks like.

You can scroll back up to our section on using boiler controls and thermostats for our expert tips to help you save money.

No motorised valves and automatic bypass valve

In essence, both of these control the flow of water from the boiler, making sure that it's not using more hot water than is needed. Automatic bypass valves are more specifically used to maintain the water flow rate when there are thermostatic radiator valves (TRVs).

Why will this cost me money? Without these, more hot water than is needed may flow through your heating system, wasting energy.

How will I know if I don't have this? Both of these comprise of a collection of pipes and joints, and motorised valves have a small box on the top - see the image below for examples. To determine whether you have them, it's worth asking an installer to take a look. 

Which heating controls work with which heating system? 

There are five main types of heating controls that can help you to save money on your heating, some of which we have mentioned above:

  • Room thermostat – measures how warm your room is and adjusts the boiler accordingly. You can get programmable or timer versions of these (see below)
  • Thermostatic radiator valves (TRVs) – allow you to adjust the temperature of individual radiators and turn them off completely.
  • Timer – turns your boiler or hot water on or off at set times, such as off when you're at work, and on ready for when you get home.
  • Programmer (see image below) – lets you set different times and temperatures for your heating and hot water for different days of the week. For example, you might want your heating to be hotter and on for longer at the weekend than during the week. You can find out more information about using timers and programmers, and see our expert tips lower down this page.
  • Smart thermostat - allows you to control the temperature in your home when you are not there, for example from your smartphone or tablet.

But not all controls will work with all heating systems. The heating controls you need will depend on the type of heating system you have - combination or heat-only - and whether or not your hot water comes direct from your boiler.

When you have a new boiler or heating component installed, you should discuss with your heating engineer the controls you need for your home . But to make sure you're well informed before you call someone in, here's what controls you should ideally have.

Controls to use with heat-only boilers

What is a heat-only boiler?

There are two types of heat-only boilers. The first are supplied by cold water from a cylinder that sits high up in your home, usually in your loft. Cold water then flows down from there to a gravity-fed hot water cylinder (as mentioned above), where it's heated and then sent around the house. 

The other type doesn't require a tank in the loft, but instead just one hot water cylinder. 

Heat-only boiler controls

To make the most of your heating and to save money, both types of heat-only system should include:

  • a room thermostat, preferably a timed or programmable one
  • a hot water cylinder thermostat
  • a hot water cylinder timer
  • hot water cylinder insulation
  • thermostatic radiator valves on all rooms except the one with the room thermostat
  • a boiler timer
  • a boiler interlock 
  • motorised valves
  • automatic bypass valve.

Controls to use with combi boilers 

What are combination boilers?

There are a few types of combination (combi) boiler, but in essence, they all take cold water directly from the mains supply and heat it when it’s needed, removing the need for any cylinders or water storage tanks. 


Combination boiler controls

With a combination boiler, you won't need any of the elements for a cylinder, as mentioned above. Instead, you'll only need:

  • a room thermostat, preferably a timed or programmable one
  • thermostatic radiator valves in all rooms except the one with the room thermostat
  • a boiler timer
  • a boiler interlock 
  • motorised valves
  • automatic bypass valve.

You can find out more about combination boilers on our dedicated combi boilers page.

Built-in boiler controls 

Built-in boiler controls are useful if your boiler is easy to access, but not if your boiler is in a loft or garage. 

Boiler on/off switch

The simplest boiler control is the on/off switch. Turning it on puts the boiler in standby mode until it needs to provide heat for your hot water or radiators, for example because you have a thermostat and the room is cooler than the say temperature. Standby uses a small amount of electricity - usually less than 10W per hour.

Some on/off switches have an option to turn on just the hot water, so you can turn the heating off permanently during summer. Keep in mind that some older washing machines and dishwashers need hot water from the boiler to run. Modern ones should heat the water within the appliance itself.

Turning off your heating will save energy, particularly if it's an old boiler with a pilot light that's always burning. It's worth turning your heating on and off on every so often over the summer, though, to make sure that valves and pumps don't seize up.

Temperature controls for your heating and hot water

Some boilers have separate controls for the temperature of the radiators and hot water. 

This allows you to set the temperature of the water that leaves the boiler to heat the house. If you lower the temperature, your boiler will operate as efficiently as possible. If you increase the temperature, you will heat your radiators more quickly in cold weather.

It's advisable to:

  • set your boiler temperature to 82°C in winter (between medium and high) and adjust down if radiators feel too hot, or up if not warm enough
  • set your boiler temperature to 65°C in summer (between medium and low) and adjust down if your water feels too hot.

If you have children, being able to control the hot water temperature is essential, as you can prevent scalding hot water from reaching the taps. It can also provide a boost in cold weather if your hot water is not quite hot enough.

If you don't have separate controls for this, it's worth speaking to a heating engineer about getting thermostatic mixing valves to regulate the temperature for your bath, shower or sinks to avoid scalding. 

Thermostatic radiator control valves (TRVs)

These detect the local air temperature and regulate the flow of hot water through the radiator, depending on how hot the room is. They do not control the boiler. They should be set to give you the temperature you want in each individual room.

TRVs usually have a bulky valve at one end, marked with * and numbers from one to five. The * setting is to protect against frost. 

It's not a good idea to have a TRV on the radiator in the same room as the main thermostat. This is because if you alter the TRV, the thermostat will adjust itself to be in line with this nearby radiator.

They need a free flow of air around them and should not be covered by curtains or blocked by furniture.

Cylinder thermostat

Like room thermostats, cylinder thermostats work by sensing the temperature of the water inside the hot-water cylinder, and switching on and off the heat supply from the boiler to the hot-water cylinder when the temperature is below or above the set temperature.  

These should always be set to between 60°C and 65°C - this is high enough to kill off harmful bacteria in the water, but not so high that it increases the risk of scalding. 

If you have a boiler control thermostat, it should always be set to a higher temperature than that of the cylinder thermostat so it can produce water that is hot enough to heat the water in the cylinder.

Advanced boiler and heating controls 

These features give you full control of your heating and make it adapt automatically to changing weather conditions.

Intelligent heating controllers

These combine several of the basic controls, and can learn how long it takes for a house to heat up in different weather conditions. They also often allow for different temperatures to be set between day and night.

Weather compensators

These measure the temperature, either internally or externally, and delay switching on the central heating on milder days.

Full zone control

Most homes have a single heating zone – the only controls in the rooms are thermostatic radiator valves (TRVs - see above).

When a new central-heating system is installed, it's possible to fit full zone control that has separate pipe loops and thermostats for two (or more) areas. This can save significant amounts of fuel in larger houses.

Smart thermostats

Smart thermostats can be controlled with a tablet or mobile phone. This means that you can adjust your heating when you are out of your home, or from the comfort of your own sofa. To find out everything you need to know about smart thermostats, including which ones are the best, see our smart thermostat guide.  

*Online survey: 1,210 Which? members, February 2017.


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