Boiler controls and thermostats

Boiler controls and thermostats

by Matthew Knight

Find out how to save money with heating controls, and discover the best heating controls for a cosy home.

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. Which will keep your home cosy and cut your energy bills.

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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. Standby uses a small amount of electricity - usually less than 10 watts 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.

Temperature controls

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

This allows you to set the temperature of the water that leaves the boiler to supply the heating. 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.

Expert heating tips:

  • set your boiler temperature to 82°C in winter (between medium and hot) 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.

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, representing a 15-minute period, that are pushed in to select when you want the boiler to turn on. 

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.

Central heating and thermostat controls

These are positioned away from your boiler and usually allow you to turn it on or off to regulate the temperature in your home. Older versions are connected by wires running to your boiler, while newer systems tend to send signals to the boiler wirelessly.

Room thermostat controls

A room thermostat switches the heating system on and off as necessary.

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

Expert heating tips:

  • setting the thermostat to 20°C is usually adequate 
  • recommended night-time temperature is 16-19°C
  • it is advisable for babies to sleep in a room no warmer than 18°C
  • the temperature shouldn't drop below 16°C for elderly people and those with impaired mobility.

Unless you have a smart thermostat that allows you to control individual radiators in your home, there's usually only one room thermostat per heating system. It controls the temperature of the whole house based on the temperature of the room it's in. It is best located in a living room or bathroom, which you'll probably want to be the warmest room in the house. 

Room thermostats need a free flow of air to sense the temperature, so make sure yours isn't covered by curtains or blocked by furniture. Nearby electric fires, televisions, wall or table lamps may stop the thermostat from working properly.

Click to find out more about smart thermostats.

Programmable room thermostat

A programmable room thermostat lets you choose what times you want the heating to be on, and what temperature it should reach while it's on. 

A seven-day timer 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.

If your heating system is a boiler with radiators, there will usually be only one programmable room thermostat to control the whole house. The time on the programmer must be correct. Some types have to be adjusted when the clocks change to and from British Summer Time.

You may be able to 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.

Programmable room thermostats need a free flow of air to sense the temperature, so they must not be covered by curtains or blocked by furniture. Nearby electric fires, televisions, wall or table lamps may prevent the thermostat from working properly.

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.

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 local radiator.

TVRs usually have a fat valve at one end, marked with * and numbers from one to five. The * setting is to protect against frost. They need a free flow of air around them and should not be covered by curtains or blocked by furniture.

Hot water controls

Cylinder thermostat

A cylinder thermostat switches on and off the heat supply from the boiler to the hot-water cylinder. 

It works by sensing the temperature of the water inside the cylinder. It switches on the water heating when the temperature falls below the thermostat setting, and switches it off once the set temperature has been reached.  

This thermostat is strapped to the outside of a hot water cylinder near the bottom. It should 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 by thermostatic radiator valves (TRVs - see above).

When a new central-heating system is installed, it's possible to fit a full zone control that has different pipe loops and separate 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. So 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. 

Save money with the best heating controls

Out-of-date central heating system components and controls can lead to wasted energy, costing you money. They can also create potential heating problems.

  • hot water cylinder supplied by gravity-fed water: stored water is slow to reheat
  • no cylinder thermostat: stored water can become too hot and risk scalding
  • no cylinder insulation: heat is wasted through the surface of the cylinder
  • no room thermostat: rooms are too hot or too cold
  • lack of thermostatic radiator valves (TRVs): excessive room temperatures and poor heating system balancing
  • no boiler interlock: this means the boiler stays hot and cycles unnecessarily during programmed heating periods.

You might not notice these issues in your home, but they'll be wasting your money in the long run.

To find out how much an inefficient boiler could be costing you, and to work out if you need a new boiler, take a look at our guide on boiler energy efficiency.

Get the best heating controls to save you money

The type of heating controls you need will depend on the type of heating system you have and whether your hot water comes direct from your boiler or via a hot water cylinder.

When you have a new boiler or heating component installed, you should discuss which controls you need for your home with your heating engineer 

There are five main types of heating control:

  • timer – turns your boiler on or off at set times
  • room thermostat – measures how warm your room is and adjusts the boiler operation accordingly
  • programmer – lets you set different times and temperatures for different days of the week
  • thermostatic radiator valves (TVRs) – allow you to adjust the temperature of individual radiators and turn them off completely
  • Smart thermostats - allow you to control the temperature in your home when you are not there

Controls to use with heat-only boilers

Your system should include:

  • programmable room thermostat 
  • separate timing capability for hot water
  • hot water cylinder thermostat
  • thermostatic radiator valves on all rooms except the one with the room thermostat
  • motorised valves - to control the flow of water from the boiler to heating and hot water circuits
  • automatic bypass valve - used to maintain a minimum water flow rate through the boiler when thermostatic radiator valves (TVRs) are operating
  • boiler interlock - a wiring arrangement to prevent the boiler firing when there is no demand for heat.

There is a lot more information on heat-only boilers in our guide to the different types of boilers, including combi boilers.

Controls to use with combi boilers 

Your system should include:

  • programmable room thermostat 
  • thermostatic radiator valves on all rooms except the one with the room thermostat
  • automatic bypass valve - used to maintain a minimum water flow rate through the boiler when thermostatic radiator valves (TVRs) are operating
  • boiler interlock - a wiring arrangement to prevent the boiler firing when there is no demand for heat.

Find out more about combi boilers.

Using heating controls effectively

Effective heating controls let you take charge of when, where and at what temperature your heating is operating. 

Simple changes that will make efficient use of your heating controls can make a big difference:

  • turning down your thermostat by just 1°C can save you £80 to £90, according to the Energy Saving Trust
  • zone your heating to the rooms you use the most, and cut your bills by reducing heating to the rooms you use the least
  • programme your heating to only work when the house is occupied
  • set your thermostatic radiator valves (TVRs) to a low temperature.

Lower heating costs: easy ways to save money

Small changes to your daily routine can keep you and your property warm without turning up the thermostat. 

Try making these simple changes and you could reduce your heating costs, save money and cut your home's carbon footprint.

  • curtains – use the natural light and warmth of the sun to keep your home warm during the day. Then close your curtains in the evening to keep that free heat inside, and to protect your room from draughty windows. Hang curtains behind your front door and draw them in cold weather
  • ventilation – letting air into your home will keep your house fresh, but try to open windows to air rooms when the sun is on them. Then keep windows and doors closed when the heating is on
  • room by room – turn the radiator down in rooms that aren’t used regularly, but regularly check for signs of damp or condensation
  • close doors – keep warm air in your main rooms by closing the door
  • add a layer – make a warm jumper, not your central heating, your first resort when the temperature drops

Lower heating costs: low-cost changes

You can also make some low-cost changes to prevent your hard-earned cash leaving your house as escaping heat.

Draught-proof doors 

Invest in some low-cost measures to insulate doors around your home and reduce your heating costs.

  • add a self-adhesive foam or rubber seal around the door cavity
  • add a threshold strip to the bottom of the door with a brush to cover any gaps
  • draught-proof your letterbox with a seal around or under the flap, and a brush inside 
  • stop cold air coming in through keyholes with a cover

Heat-reflective foil 

Fit this behind radiators on outside walls with the shiny side facing into the room. This reflects heat from the surface of the radiator into the room and away from the wall.

Seal draughty gaps 

Fill any gaps between skirting boards and the floor. This can be done with wood molding or flexible silicon sealant.

Loft hatch insulation 

Insulate the loft hatch with a strip of foam or rubber seal.

Insulate your hot water cylinder

Unlagged cylinders lose heat from their surface.

Put a cylinder jacket over an uninsulated cylinder to prevent this heat loss.