Heating Controls

Heating Controls: The Full UK Guide to Thermostats, TRVs and Zoning

Heating controls are the parts of your system that decide when the heating runs, how warm each room gets and when hot water is ready. A full set, as defined by gas network guidance, includes a programmer, thermostatic radiator valves and a room thermostat¹. Independent advice describes the same minimum for a central heating system: a programmer for time control, at least one room thermostat, and thermostatic radiator valves on the radiators². Without them, a boiler runs flat out whenever it is switched on, heating rooms nobody is in and water nobody is using.

The payoff is real but modest. Installing and using a full set of heating controls could save £110 a year where a system previously had no controls¹, and independent figures put the saving at £100 a year in Great Britain and £110 in Northern Ireland². Adding the full set from scratch costs around £600, or around £370 if a programmer and thermostat are already in place². Controls are also a regulatory matter: building guidance for new dwellings and boiler replacements requires thermostatic room controls in each room³, and heat pump systems must have adequate controls⁴.

For a household working towards energy independence, controls matter in two directions. They cut the fuel a home burns for the warmth it actually wants, which shrinks both the bill and the exposure to price rises. But they also add a layer of dependence of their own: a smart thermostat that runs through an app depends on Wi-Fi, a manufacturer's servers and the maker's continued support, while a basic programmer and mechanical thermostat depend on nothing beyond the wiring in your walls. This guide covers both kinds, and the trade-offs between them.

The purpose of heating controls and what a complete setup includes

A heating control system is a chain of decisions. The programmer decides when the system is allowed to run. The room thermostat decides whether it needs to, by measuring the temperature in one reference room and switching the boiler off when the target is reached. Thermostatic radiator valves decide, room by room, how much hot water each radiator receives, closing automatically as a room reaches its set level⁶. Together they replace the single question "is the boiler on?" with three: when, how warm and in which rooms.

The regulatory baseline reflects that chain. Guidance under Approved Document L states that for heating systems in new dwellings, or when a heat generator such as a boiler is replaced in an existing dwelling, each room should be provided with thermostatic room controls able to separately adapt the heating output in each room served⁷. The same document requires that heat pump systems have adequate controls⁴. Electric systems are covered too: for electric panel heaters, in new systems or when components are replaced, time and temperature control should be provided for separate control of each room or each appliance³.

Controls are not a niche purchase. Under the Energy Company Obligation, heating controls were recorded as a delivered measure 514,780 times in the public reporting data⁸, which makes them one of the most commonly installed energy efficiency measures in the scheme. That scale reflects how many UK homes historically ran with little or no control, and how much a basic set changes how a system behaves.

The full set is described the same way by the gas network and by independent advice: a programmer, thermostatic radiator valves and a room thermostat¹. What that set does for independence is straightforward: it stops the home burning gas, oil or electricity for heat that nobody wanted. What remains dependent is the heat source itself. Controls govern a boiler; they do not replace it, and a home with a gas boiler and perfect controls still buys every unit of gas it burns. The pages on heating controls and energy independence cover that boundary in detail.

Room thermostats: their operation and best positions

A room thermostat is a switch with a thermometer in it. It measures the air temperature in the room where it is fitted, compares that with the setting, and calls for heat until the target is reached, then tells the boiler to stop. Because it works from air temperature rather than radiator temperature, it responds to warmth from the sun, cooking and the people in the room, not just to the heating itself. The practical setting advice is to use the lowest comfortable temperature, which for most people is between 18°C and 21°C².

Placement is what makes a thermostat honest or useless. It has to sit in a room that represents how warm the home actually is, which is why the guidance on thermostatic room controls is written around each room being able to adapt its own heating output⁷. A thermostat in a room that is always warm for other reasons, such as a kitchen with an oven running, will shut the heating off before the rest of the house is warm. One in a cold hallway keeps the boiler running after the living rooms are baking.

The saving from the thermostat setting itself is well evidenced. Turning it down by just one degree, from 22°C to 21°C, could save £120 a year in Great Britain and £80 in Northern Ireland². Official advice in Northern Ireland puts the same single degree at as much as 10 per cent of heating bills⁵. The thermostat is therefore the single highest-leverage control in the house: one dial, one degree, a tenth of the bill.

There is a rule that governs how a thermostat relates to the valves on radiators, and it comes from the building regulations guidance rather than custom: thermostatic radiator valves should not be used in the same room as the thermostat, and heat emitters in the same room as the thermostat should have manual controls⁷. The reason is mechanical. If the radiator in the thermostat's room has a TRV and that TRV closes first, the thermostat never sees the room warm up and keeps the boiler running with every other radiator shut. The pages on room thermostats and wired vs wireless thermostats cover the types and siting choices in depth.

Thermostatic radiator valves: individual room control for roughly £10

A thermostatic radiator valve is a self-contained thermostat strapped to a radiator. It controls the temperature of each room by opening and closing automatically to control the flow of hot water through the radiator it is fitted to⁶. The head can also be manually adjusted to different settings to control the flow⁶, which is how most people use them day to day: turn the spare room down, turn the bathroom up.

Two characteristics define what a TRV is and is not. First, it has no communication with the boiler⁶. It opens and closes its own radiator and nothing else; it cannot tell the boiler to modulate, cannot report a temperature and cannot be seen by the rest of the system. Second, it is a per-room device, which is exactly where its value lies. Lowering the thermostatic radiator valves can reduce demand in rooms that are not in use⁹, and a TRV gives better control over the individual room temperatures¹⁰.

The rules on TRVs are unusually clear. Building regulations guidance for energy efficiency work states that any new radiator installed will require a thermostatic radiator valve to be installed¹¹, and the same requirement appears in guidance for extensions and additional storeys¹⁰. It is also encouraged, though not required, to place TRVs on existing radiators¹⁰. TRVs have also been eligible measures under government voucher schemes¹², which has kept their installed price low. The one room where a TRV must not go is the room containing the room thermostat, which takes a manual control instead⁷.

There is a smarter version of the same idea. Programmable TRVs add timing control, letting each radiator come on at different times and heat each room to its own schedule². These are covered in full on the smart TRVs page, and the question of whether they earn their price is examined at do TRVs save energy. The basic valve, though, does the essential job: it stops each room being heated to the temperature of the warmest room in the house.

Programmers and timers: warmth only when the house is in use

A timer or programmer controls when the heating comes on and off². That is the whole function, and it is the one that most homes lack discipline over. A programmer splits the day into heating periods, typically morning and evening, and holds the system off outside them. Without one, the choice is between the boiler running all day and someone remembering to turn it off, and human memory is the least reliable control in any home.

The principle extends into smart territory. Official sustainability guidance for self-build homes advises installing smart systems that control lighting, heating and cooling based on occupancy and time of day¹³. The same logic applies to an existing home: the aim is for the heating to follow the household's actual pattern rather than a guess at it. Some smart controls know when the household is away, might adjust the heating accordingly, or send a message so the heating can be turned off via an app¹⁴.

A programmer's value depends on it being set to the real pattern of the home, and on being revisited when that pattern changes. The common failure is a schedule set once, years ago, heating empty rooms at 7am for a household that now leaves at 8:30. The pages on heating programmers and timers and how to use a heating programmer to save energy cover setting and adjusting them, and heating schedules and setback covers the question of whether to leave the heating on constantly.

One limit is worth stating. Smart thermostats, as a category, only allow tracking of the heating itself, so a household cannot keep an eye on electricity and gas usage through them¹⁵. A programmer, smart or otherwise, governs the heating; it does not give the whole-house picture that a smart meter display does. For households trying to understand total consumption, the two devices answer different questions.

Smart thermostats: remote apps, learning features and geofencing

A smart thermostat connects to your Wi-Fi so you can control your heating and hot water through your smartphone, tablet or desktop¹⁵. Most smart heating controls link to your phone, and heating can be controlled via smartphone, tablet or laptop, or by telling a smart speaker what you want¹⁴. Beyond that base function, what a model offers varies: depending on the model, a smart thermostat may allow app control, voice control, hot water settings, location-based heating, reminders or alerts, open window detection, routine learning and heating-use tracking¹⁶.

The learning and location features are what separate smart from merely remote. These devices may interpret inputs such as preferred room temperature, learn from what the household does, and react to other data like weather forecasts; some have a learning function that predicts behaviour from how the heating is set and adjusted and how the home is occupied¹⁴. Location-based heating, often called geofencing, uses the phone's location to decide whether anyone is home. Some controls know when the household is away and adjust or message accordingly¹⁴.

Before buying, the advice is to check that a smart thermostat is compatible with your boiler and heating system, usually in the product description or on the thermostat manufacturer's website¹⁶. Compatibility is not universal across boilers and system types, and it is the single most common purchase mistake. The question is examined model by model at smart thermostat boiler compatibility.

The cost structure is different from dumb controls. If you want a smart thermostat, you may have to pay for the device and the installation¹⁵, and there is no grant route comparable to the subsidised TRV installations under the energy company obligation. There is also a dependence to weigh: an app-controlled thermostat depends on the manufacturer's servers, app and continued support in a way a wall-mounted programmer never does. The smart thermostats page covers the category, smart thermostat subscriptions covers ongoing charges, and smart heating control security and data covers what the device knows about you.

Zoning: single or dual zones, and the role of 150m2

Zoning means splitting the heating into independently controlled circuits, each with its own time and temperature control, so that part of the house can be heated without the rest. The rules draw a line at floor area. For wet heating systems in new dwellings with a floor area of 150m2 or greater, a minimum of two independently controlled heating circuits should be provided⁷, a requirement restated in the English guidance³.

Below that threshold the picture varies by system and by nation. Scottish guidance allows that dwellings with a total floor area of 150m2 or less may have a single space heating zone with independent time control, provided there are TRVs on radiators outside the reference rooms or electronic temperature control¹⁷. The same Scottish guidance requires at least two space heating zones with independent temperature and time control for dwellings above 150m2, including for solid fuel systems¹⁷. Draft Scottish guidance goes further for smaller homes: dwellings under 150m2 should have at least two space heating zones with independent temperature control, one assigned to the living area¹⁸.

Northern Ireland has its own rule. Technical Booklet F1 states that central heating systems should be provided with a minimum of two independent heating zones, each controlled by a room thermostat, with thermostatic radiator valves on radiators in rooms without a thermostat, except bathrooms¹⁹. So a home in Northern Ireland may need two zones where the same floor area in Scotland could run on one, and the difference is worth knowing before planning work. The heating zoning page sets out each nation's requirements, and heating controls wiring covers the zone valves and wiring centres that make it happen.

Zoning is where controls start to cost real money, because each zone needs its own valve, thermostat and wiring. It is also where the savings logic is strongest in larger homes: a five-bedroom house heating only the ground floor on weekday mornings burns materially less than one heating everything. For a small flat, a single zone with good TRVs achieves nearly the same result at a fraction of the cost, which is why the regulations allow it.

Costs and savings of a full set: about £600 fitted, £100 yearly

The installed costs are straightforward. If a home has no heating controls, adding a programmer, thermostat and TRVs on all radiators costs around £600. If a programmer and thermostat already exist, adding TRVs to all radiators costs around £370². Those are independent figures for typical installations; actual prices are installer-quoted and vary with the number of radiators and the wiring involved.

The savings figures come from several directions and are worth reading together. Installing and using a full set of heating controls could save £110 a year where the system previously had no controls¹. Independent advice puts it at £100 a year in Great Britain and £110 in Northern Ireland². Turning the thermostat down one degree adds as much as 10 per cent off heating bills⁵, or £120 a year in Great Britain and £80 in Northern Ireland for a single degree from 22°C to 21°C². One local authority source goes further, suggesting that reducing the thermostat by one degree could save up to 25 per cent of heating bills and associated carbon¹². The figures differ because they measure different things: a full controls installation saves more than a one-degree change alone, and percentage savings depend on how warm the home was to begin with.

For electric heating, the official consumer protection guidance models the savings by control level: for a large house with high usage, around £300 per month, low control saves 2 per cent of the heating bill (£6 per month), medium control 4 per cent (£12 per month) and high control 6 per cent (£18 per month)²⁰. Those are modelled examples rather than guarantees, but they show the shape of the relationship: better control saves a few per cent of the bill, not half of it.

Set against a £600 installed cost, a £100 annual saving repays the investment in about six years, and the controls typically outlast that, since a boiler's current lifespan is around 15 years²¹ and controls are replaced far less often. The heating controls cost page breaks the costs down by component, and do heating controls save money tests the savings claims against the evidence.

Temperatures and settings: 18 to 21°C by day

The comfort range is consistent across the sources. A thermostat should be set between 18°C and 21°C to keep the household safe and well¹, and independent advice says the same: set the thermostat to the lowest comfortable temperature, which for most people is between 18°C and 21°C². The operative phrase is "lowest comfortable": the saving comes from the gap between the temperature a home is set to and the temperature its occupants actually need, and every degree of that gap is worth roughly 10 per cent of the heating bill⁵.

Hot water has its own setting. The temperature of the hot water thermostat should be set between 60°C and 65°C². That range balances two things: water stored below 60°C carries a legionella risk, and water stored hotter scalds and wastes the fuel used to heat it. The hot water controls page covers cylinder thermostats and how they interact with the programmer's hot water channel.

Room-by-room settings are where TRVs earn their place. Lowering the thermostatic radiator valves reduces demand in rooms that are not being used⁹, so the common pattern is living spaces at the comfortable setting and spare rooms, hallways and landings a notch or two lower. The thermostat temperature settings and room temperatures pages give recommended levels for each room type.

Two practical habits keep the settings honest. First, change them with the seasons: a setting that was right in January is too high in April. Second, treat the thermostat as a ceiling, not a target to be raised when a room feels cold, because the usual cause is a radiator that needs bleeding or a TRV that is shut, not a house that needs to be hotter. Radiators should be bled at least once a year, and preferably every few months²².

The limits of controls: compatibility, siting and the TRV-thermostat rule

The limitations of heating controls are consistent and worth stating firmly, because several of them cannot be fixed by buying a better model.

• The TRV-thermostat rule. Thermostatic radiator valves should not be used in the same room as the thermostat, and heat emitters in that room should have manual controls⁷. A TRV in the reference room closes, the thermostat never reaches its target, and the boiler runs on.
• TRVs are blind. They have no communication with the boiler⁶. A house full of closed TRVs with a running boiler is a system with no way to tell itself to stop, which is what the boiler interlock arrangement exists to prevent.
• Smart compatibility is not universal. A smart thermostat must be checked against the specific boiler and heating system before purchase¹⁶.
• Smart controls track heating only. They do not let a household monitor gas and electricity usage¹⁵.
• Room controls have a technical limit. Thermostatic room controls may not be technically feasible in dwellings with low heat demand, for example less than 10W/m2, or in dwellings with buffer zones with high thermal mass⁷. A very well insulated home may simply not need per-room control.
• Hybrid systems lack agreed standards. There is currently no agreed control specification or inclusion of hybrid control systems in standards²³, which leaves hybrid heat pump installations dependent on individual manufacturers' approaches.

Low-temperature systems add a further control requirement: controls must be installed that ensure the heat generator does not supply hot water services and space heating service simultaneously²⁴. That is a design constraint rather than a fault, but it shapes what a control upgrade on a low-temperature system involves.

None of these limits undermine the case for controls; they define what a realistic upgrade achieves. A full set makes an existing system behave sensibly. It does not make an inefficient boiler efficient, an undersized radiator large, or a poorly insulated house cheap to heat, and a household expecting it to do so will be disappointed.

Fitting and upgrades: who installs controls and the rules that apply

The regulatory position on installing controls is lighter than many expect. Planning permission is not normally required for the installation or replacement of a boiler or heating system if all the work is internal²⁵. On the building regulations side, if a heating or hot water system is to be replaced, a building control application may not be required, and where one is required it may not be necessary to apply in advance of the work²¹. If an existing system has been altered or replaced, the person who last worked on the system is responsible for its safe running and should issue a certificate showing the necessary checks have been carried out²¹.

For heat pump work, the requirements are more formal. The installer should give notice to the building control authority that commissioning has been carried out in accordance with the approved document, and the certificate, or a copy of the information on it, must be given to the building control authority⁴. It is advisable to contact an installer who can provide the necessary advice, preferably one who belongs to either the Microgeneration Certification Scheme or the relevant Competent Person Scheme²⁶.

For the purchase itself, the advice is consistent: get quotes from at least three different installers to make sure you are getting value for money, and make sure the installers are certified with a scheme like TrustMark². Those two habits, comparison and certification, are the householder's main protection in a market where prices are quoted rather than published.

One recent change affects what installers must do under the Energy Company Obligation. The requirement for a full set of heating controls in the property following a boiler installation was removed in the ECO4 delivery guidance²⁷. That is a rule about a subsidy scheme rather than about building regulations, so it changes what a funded installation must include, not what a good one should. The building regulations requirement for thermostatic room controls when a boiler is replaced still stands⁷.

Maintenance of the control system itself is minimal, but the radiators it governs are not. Bleed radiators at least once a year, preferably every few months; bleeding should only become a concern if it is needed one or more times a month, or if it has no effect at all, and both cases warrant professional help²². The heating controls installation page covers the process in order, and heating controls faults covers what goes wrong.

Using controls with heat pumps and low-temperature radiators

Heat pumps change the control problem in two ways. First, the regulatory baseline is the same in kind: heat pump systems must have adequate controls⁴. Second, the physics is different: a heat pump is most efficient running steadily at a low flow temperature, so the on/off switching that suits a boiler suits it less well, and the control set that works best is one that modulates rather than one that toggles. That is what weather compensation and load compensation do, and why the OpenTherm protocol matters for modulating control.

Hybrid systems, which pair a heat pump with a boiler, have a specific control gap. Heat pump and hybrid controls can be fitted to different heat sources and boiler types, such as regular or combination boilers²³, so the hardware is adaptable. But there is currently no agreed control specification or inclusion of hybrid control systems in standards²³, which means the logic that decides when the boiler runs and when the heat pump runs is set by each manufacturer rather than by a common standard. A household buying a hybrid system is buying into that maker's control philosophy, and should treat the question of how the two heat sources are orchestrated as part of the purchase.

Low-temperature systems also carry the simultaneous operation rule: where the heat generator provides hot water, controls must be installed that ensure it does not supply hot water services and space heating service simultaneously²⁴. And the room-control requirement has its exception at the low-demand end: thermostatic room controls may not be technically feasible in dwellings with low heat demand, less than 10W/m2, or with buffer zones of high thermal mass⁷, which in practice covers many well insulated new builds.

TRVs have a specific relationship with heat pumps, and it is a contested one: many heat pump installations leave them off, and the reasons are covered at TRVs and heat pumps. The underfloor heating controls page covers the manifold and wiring arrangements that low-temperature underfloor systems use instead.

UK manufacturers and product ranges

The UK market for heating controls is broad, spanning long-established thermostat and timer makers and newer app-first brands. This site carries dedicated pages for most of them, including tado°, Hive, Google Nest, Drayton Wiser, Honeywell Home, Heatmiser, Netatmo, Bosch, Vaillant, Worcester Bosch, Viessmann, Danfoss, Salus, EPH Controls, Sangamo, Horstmann, Ideal, Baxi, Grant, NIBE, Warmup, Dimplex, Elnur, Rointe, Herschel, Myson, and open-source routes through Home Assistant, Shelly and SONOFF. Head-to-head pages such as Nest vs Hive, tado° vs Hive and evohome vs tado° compare the leading smart ranges directly.

The maker-verified specifications available for this page are limited to one smart home device, which illustrates the direction the wider market is taking. The Roomer Smart 12, a residential smart dehumidifier, is specified by its maker at a noise level of no more than 36 dB(A), using R290 refrigerant²⁸. It is not a heating control, but it is representative of the app-connected environmental devices now sold alongside thermostats and TRVs, and a reminder that a "smart home" heating setup often pulls in equipment from beyond the heating aisle.

When choosing between brands, the same rules apply as for any controls purchase. Check compatibility with your boiler and heating system before buying¹⁶. Get quotes from at least three installers, certified with a scheme like TrustMark². And weigh what each brand's product depends on: a control that runs through a manufacturer's cloud depends on that company staying in business and supporting the app, a consideration covered at smart heating control security and data and Nest thermostat UK availability.