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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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One in four of you* have told us that you believe 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. This will keep your home cosy and cut your energy bills.

In this article:

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

Top tips for using boiler controls and thermostats 

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, walls or table lamps, as these may stop the thermostat from working properly.

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

Mechanical boiler timers explained

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.

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, or a smart thermostat.

Using 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 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. 

Zoned heating: the most efficient setup 

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.

Which heating controls work with which heating systems? 

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, but not all controls will work with all heating systems. 

  • 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.

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. 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. 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.

See the best heat-only boilers as voted for by owners and heating engineers. 

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. 

Combi boiler controls

  • 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 and the best brands on our dedicated combi boilers page.

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 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 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.

If you want to find the most efficient boiler for your home, read our guide on how to buy the best boiler.

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. 

What advanced boiler and heating controls are available? 

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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