Boiler controls and how they can save you money

Controlling when your boiler is on and how hard it's working can save you money on your heating bills, but many domestic boilers are only set up to be on or off. 

Modern condensing boilers can operate at a range of outputs and, when not running at maximum temperatures, actually recover some heat to run more efficiently. Until fairly recently, however, many boilers in the UK tended to have basic controls that switched them on for short bursts of intense heating then simply turned them off again, without making use of the range of output levels boilers are capable of. 

In 2018, Boiler Plus legislation was introduced to tackle this problem by requiring an energy-saving control to be set up during new boiler installations. But there's still a lot of leeway within the regulation to allow for inefficient set-ups. 

Below are some of our top tips to make sure your boiler's set up to be as efficient as possible and save you money on your monthly gas bill – this could be as much as 10% or more.  

Will your boiler let you down during a cold snap or mid-shower? Our unique research reveals the most reliable boiler brands.

What boiler controls will save me money?

Boiler Plus sets out three boiler control types that help you to save money.

• Smart controls automate your system so your boiler only comes on at optimum times. They use features such as geofencing, which detects when you're out and so don't need the heating on, and open-window detection to make sure your home's only heated when it's insulated. 
• Load compensation controls lower the flow temperature your boiler is running at to a level that's sufficient to reach the temperature set on your thermostat, reducing heat wastage.
• Weather compensation controls adjust your boiler's output according to need, based on a sensor that detects how cold it is outside.

These are all better alternatives to basic controls and manual timers, and you'll usually need to consider fitting one of them if you get a new gas boiler installed. 

Although the Boiler Plus standard is fairly new, minimum efficiency standards for boilers were made law in 2005 when new boilers became condensing. Boiler Plus strengthens these.

What is a smart thermostat?

The 'smart' in smart thermostat simply means internet-connected. This opens up functionality you can't get with traditional thermostats, such as location tracking, remote control and monitoring of your heating patterns. 

Some smart thermostats just work like traditional on/off controls and don't enable a boiler to modulate itself. Others, such as the Google Nest and Tado smart thermostats, can be set up by an engineer to modulate your boiler and work as a compensating thermostat, which can save more energy – more on this below. 

Read our smart thermostat reviews to find a model that's accurate and easy to use. 

What are compensation controls?

We've been encouraging people to lower the flow temperature of their combi boiler since before energy bills increased sharply in October 2022 – guidance that was later issued by the government in December 2022. 

This is because boilers can heat the water that goes to your radiators to different temperatures, and when the flow temperature is adjusted down, you can use less energy while increasing the amount of heat your boiler can recover – heat that's otherwise pushed out of the flue. 

You can adjust it manually – find out more by reading our guide to adjusting your boiler flow temperature – but a load or weather compensation system does it automatically. These determine how much heat your boiler needs to create, and sets the temperature accordingly ⁠so it's using no more or less energy than necessary.

This is fairly precise work, and while it's possible to guess the right temperature setting to use by looking at the boiler's control panel, it's best if an engineer sets up the boiler to work it out automatically.  

How do I get compensation controls?

There isn't a universal standard that governs boilers and thermostats yet. You'll need to make sure you have a boiler that can communicate with compensation controls; this will depend on the model.

Your installer should be able to tell you what controls are compatible with your boiler, and fit them. If you get weather compensation, a sensor may need to be placed outside your home. 

The most common boiler-controller language is known as OpenTherm, and this is already used by smart thermostats such as the Google Nest.

Be aware that some smart thermostats don't allow for modulation in any capacity, and simply operate boilers using on/off controls that don't save energy. An example of this is the Hive thermostat installed by British Gas.

Are there limits to compensation controls?

Boiler controls are just one part of an interdependent heating system. They won't make everything perfect, but they'll help you get the most out of your boiler according to what's feasible in your home. 

Efficient hydronic central heating systems (those that use hot water to heat your home) use low flow temperatures in properties that have large radiators and good insulation. 

Homes with small and fairly old radiators will probably only be able to go so low before the boiler will struggle to meet the temperature the thermostat demands. And with 'slow and low' heating, heat loss needs to be mitigated or the home will never reach the desired temperature, and the system will be pushed to its limits.

For your heating system to be as efficient as possible, you must also have a boiler that's the right size for your home. Boilers can work at a range of temperatures, but large boilers capable of producing significant amounts of heat will have higher minimum outputs, which means they can only ration so much. 

To give yourself the best chance of getting a boiler that can save you money on your heating bills, get an installer you trust to fit a boiler that's the right size for your home and ask whether you can have compensation controls fitted.

Should I leave my heating on 24 hours a day?

Avoid following any blanket rules for how long your central heating should be on for, as this will depend on your home. What works for a home that's highly energy efficient might not be best suited to one that isn't. 

The rise of high-efficiency heating in UK homes, helped by compensation controls and cost-effective options such as underfloor heating and big radiators, has led to more people keeping their heating on all the time. They can then use programmers to request lower temperatures during the night and when homes are unoccupied, so less energy is used.

This is a great way to heat your home when your central heating system can provide small amounts of heat. To raise the temperature, only small adjustments are needed. This kind of heating is often used in shops and offices. But if you rely on intermittent heating, such as a gas boiler running at high flow temperatures (55°C+) that's on for an hour in the morning and a few hours in the evening, this style of 24/7 heating might not be suitable.

A heating engineer can advise you on the best method of heating your specific home. If it's not very energy efficient and your radiators need to be very hot for the temperature to reach a comfortable level, you're probably better off using your heating during the hours you need it most.

If you have a smart meter, you can experiment by adjusting your programmer and looking at the difference between the amount of energy you use with intermittent and 24-hour use, but make sure you experiment on two days that are similar in temperature. 

Top tips for using boiler controls and thermostats

Standard heating controls

Heating controls that are common in UK homes include:

• a dial thermostat on your wall that turns the boiler on when the room it's in drops below the temperature it's set to (generally used in conjunction with a timer) 
• timers that let you choose the times of the day the boiler turns on and off
• programmers that let you pick a schedule for the entire week – these are a lot more customisable than simple timers, but they're harder to configure.

Adjusting 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, wall lights or table lamps, as these might stop the thermostat from working properly.

It's best to install a room thermostat in the room you want to be warmest, such as the living room.

Using built-in boiler controls

Built-in boiler controls are useful if your boiler is easy to access, but not if it's 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, when the room becomes cooler than the temperature set on the thermostat. 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 the summer. Bear in mind that some older washing machines and dishwashers need hot water from the boiler to run. Modern ones usually heat the water within the appliance itself.

Turning off your heating will save energy, particularly if you have an old boiler with a pilot light that's always burning. It's worth turning your heating on and off 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. 

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 isn't 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 fitted to regulate the temperature of the water going to your bath, shower or sinks to avoid scalding.

Temperature tips

• Setting your thermostat to 18 or 19°C is usually adequate. 
• The recommended night-time temperature is 16-19°C.
• Avoid turning up the thermostat if possible. According to the Energy Saving Trust, for every degree you increase the temperature, your heating bill will increase by about 10%.

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

Which heating controls work with which 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 directly from your boiler. Read about the different types of 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. 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 boiler. The first is 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, where it's heated and then sent around your home. 

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 in all rooms except the one with the room thermostat
• a boiler timer
• a boiler interlock 
• motorised valves
• an automatic bypass valve.

See the best boiler brands as voted for by owners and heating engineers. 

Controls to use with combi boilers

What are combination boilers?

There are several 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. 

Combi boiler controls

These should include:

• room thermostat
• thermostatic radiator valves in all rooms except the one with the room thermostat
• boiler timer
• boiler interlock 
• motorised valves
• automatic bypass valve.

Signs that your heating might not be efficient

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 having to fork out for expensive boiler repairs. 

Learn more about what your 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's then funnelled down when needed, using gravity, to a hot water cylinder below. From there, it's heated by the boiler 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 storage tank 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 isn't 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. 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, check 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 off the heating within the cylinder 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's a risk of the 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. If your cylinder has one, you'll be able to see it on the outside, around a 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. Look at the image below 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 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 could flow through your heating system, wasting energy.

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