What is a Smart Thermostat?

A smart thermostat is a heating control that connects to the internet, usually through your home Wi-Fi or a separate hub. It still performs the basic job of a room thermostat—asking the boiler for heat when the room is cooler than the set temperature—but it also lets you view and change settings through an app.

That simple definition matters because “smart” is sometimes used rather loosely. A smart thermostat is not the boiler, it does not make a poorly maintained heating system healthy, and it cannot heat a cold house without using energy. What it can do is make timing and temperature control easier, especially when your plans change.

What parts make up a smart thermostat?

Most UK boiler systems use two or three components:

• The room thermostat measures the temperature where it is positioned and gives you local controls.
• A receiver or Heat Link connects to the heating controls near the boiler, programmer or wiring centre. This is the component that passes the thermostat’s request to the heating system.
• An app, hub or cloud connection lets you change schedules and temperatures away from the thermostat. Some products connect directly to Wi-Fi; others use a bridge or hub.

The exact arrangement depends on whether you have a combi boiler, a system or regular boiler with a hot-water cylinder, more than one heating zone, or separate underfloor heating. A product described as “wireless” may mean the room unit communicates wirelessly with its receiver; the receiver itself usually still needs electrical wiring.

How is it different from a standard dial thermostat?

A traditional dial room thermostat normally has one main job: turn the heating demand on when the room is below the chosen temperature and off when it reaches it. A separate timer or programmer decides when heating is available. It can be dependable and easy to understand, but it cannot normally be changed from your phone or adapt a schedule when you are away.

A digital programmable room thermostat combines time and temperature in one control. For example, it might target 20°C in the morning, 16°C during the working day and 19°C in the evening. This can deliver most of the practical benefit many households need, without internet access.

A smart thermostat adds remote control and may add features such as geofencing, learning, weather data, usage history or multi-room accessories. The important difference is convenience and automation—not a new source of heat.

Is a Boiler Plus thermostat already smart?

Not necessarily. Boiler Plus is the English standard for heating controls fitted with replacement domestic combi boilers. Depending on the installation, compliance can be achieved with controls that improve efficiency through load compensation, weather compensation, smart automation or other accepted measures. A modern programmable or modulating control can therefore be sophisticated without offering phone control.

If your existing control already provides a clear schedule and suitable modulation, replacing it purely to gain an app may not transform your energy use. If you regularly forget to adjust the heating, return home at unpredictable times or find the existing programmer hard to use, a smart control may be much more useful.

What can a smart thermostat do?

Control heating from your phone

You can usually change the target temperature, boost the heating and edit the schedule in the manufacturer’s app. This is useful when you are delayed, working from home unexpectedly or returning from a trip.

Use a more flexible schedule

Smart controls make daily time-and-temperature periods easier to see and alter. The saving comes from avoiding unnecessary heating, not from the app itself. Energy Saving Trust says the benefit depends on how well you currently control your heating.

Respond when the home is empty

Some systems use phone location or occupancy information to suggest or make an away adjustment. This is commonly called geofencing. It is optional, and households should check how the feature behaves when several people live at the property.

Learn or optimise warm-up times

Some thermostats learn how quickly a home warms and start the boiler at an appropriate time to reach the scheduled temperature. Others learn repeated manual adjustments. “Learning” does not mean the control knows every household preference immediately; it still needs sensible settings and may need corrections.

Control hot water

Homes with a hot-water cylinder need the correct multi-channel product if they want app control of both heating and stored hot water. A single-channel combi-boiler kit may not be suitable. Google says its third-generation Nest Learning Thermostat can schedule cylinder hot water, while product choice in other ranges depends on the heating layout.

Add room-by-room control

Some systems work with smart radiator thermostats so different rooms can have separate schedules. This can be valuable in a larger home with rooms used at different times. It also adds cost and complexity, and the system design must still allow the boiler and radiators to operate correctly.

Does a smart thermostat make a boiler more efficient?

It can help the heating system use less energy if it improves the way you schedule and control heat. Turning down unused periods, avoiding overheating and using the lowest comfortable setting are the real mechanisms.

Some boiler-and-control combinations can also use modulation. Instead of giving only an on/off command, a compatible control can ask a compatible boiler to reduce its output as the home approaches the target temperature. OpenTherm is one communication method used by some third-party controls, but compatibility is not universal. Manufacturers may use their own communication systems, and an installer should confirm what your exact boiler and wiring support.

A smart thermostat cannot compensate for radiators full of air, poor system balancing, sludge, a badly positioned sensor or a boiler fault. It also cannot promise a particular saving: the result depends on the home, weather, previous settings and household behaviour.

Mainstream UK examples

Google Nest

Nest is not defunct in the UK. As checked in September 2026, Google’s UK Store still lists the third-generation Nest Learning Thermostat at £219. It learns adjustments, offers app control, includes a Heat Link and supports OpenTherm on compatible systems. Google also lists the simpler Nest Thermostat E at £199. Availability can change, so check the current store and compatibility tool rather than relying on an old review. 

Hive

Hive’s current range includes the main Hive Thermostat and the lower-cost Hive Thermostat Mini. Both provide schedules, app changes and heating boosts. Some enhanced analysis and automation features sit within the optional Hive+ service, so compare the included functions with the paid extras before choosing.

Honeywell Home by Resideo

The Honeywell Home range spans simple dial and digital thermostats through to T6 smart controls. The T6 family offers app control, scheduling and options such as wired or wireless room units. It is a useful reminder that “Honeywell thermostat” describes many different products; the model number matters.

ESi Controls

ESi offers familiar dial controls, programmable room thermostats and smart products. Its current smart range includes products such as Stratus and Mistral, while older homes may have Series 5 or Series 6 controls. ESi’s official information shows that some models can work as conventional RF controls if Wi-Fi is unavailable, and selected models support OpenTherm.

Drayton Wiser and tado°

Wiser is designed as an expandable system, with different kits for combi boilers, stored hot water and multiple heating channels. tado° also offers boiler starter kits and room-by-room radiator controls. With either system, identify the correct starter kit first; an add-on thermostat or radiator head is not necessarily a complete boiler-control package.

What happens if the internet goes down?

A properly selected control should retain basic local heating operation, but app access and some automated features may be unavailable. Behaviour varies by product. Ask what still works without broadband, whether the schedule is stored locally, and whether the thermostat has usable physical controls. This is especially important for anyone who does not want heating operation to depend on a phone.

Do you need a smart thermostat?

A smart thermostat is likely to suit you if remote changes, easier scheduling or future multi-room control would genuinely be used. A straightforward programmable thermostat may be better if your routine is stable, you prefer physical buttons and do not want another app or online account. A basic dial thermostat can still be appropriate where simplicity is the priority, provided the wider system has suitable time control.

Check compatibility before buying

• Is the boiler combi, system or regular?
• Is there a hot-water cylinder to control?
• How many heating zones are wired?
• Does the boiler accept simple on/off control, OpenTherm or a manufacturer-specific bus?
• Is there a suitable receiver location and power supply?
• Will everyone in the home be comfortable using the app and the physical control?

Controls connected to a gas boiler and mains wiring should be selected and installed by a suitably competent professional. Do not remove a boiler case or guess at control terminals. If your thermostat already says heating is on but the boiler does not fire, diagnose that fault before buying a replacement control.

Related boiler-help guides

• Do smart thermostats work with older boilers?
• Why is my thermostat not communicating with my boiler?
• Thermostat says heating is on but the boiler is not firing
• How do I programme my Hive thermostat?