Which smart thermostat should I choose, and can it work with my heating?

Will a smart thermostat work with my boiler?

Usually, yes. Most smart thermostats can switch a gas combi or system boiler on and off, which is how most older thermostats work too. The details that matter are your boiler type and how your current controls are wired.

A combi boiler heats water on demand, so the thermostat only needs to control the heating. A system or regular boiler with a hot water cylinder also needs hot water control, so you need a thermostat that can run both, or you keep a separate programmer for the water.

The quickest check is the brand's online compatibility tool, plus a look at your boiler's manual. A photo of your current thermostat, any programmer and the boiler's control panel usually tells an installer what you have.

Combi boiler

Heating control only; hot water is on demand.

System or regular boiler with cylinder

Needs heating and hot water control.

Wired or wireless: which type do I need?

It depends on what you have now. If there is a wired thermostat on the wall, a wired smart thermostat can often replace it using the same cable. If not, a wireless thermostat talks to a receiver fitted at or near the boiler.

Many smart kits come with two parts: the thermostat you see on the wall, and a receiver or hub that does the switching. The receiver often replaces your old programmer or timer, using its wiring. Where there is no programmer, it is wired into the boiler's control circuit.

Wireless thermostats can be moved around the house, which helps if your old thermostat is in a cold hallway or next to a radiator. Wired ones need no batteries and never lose their signal.

What is OpenTherm, and does it matter?

OpenTherm is a way for a thermostat to tell the boiler how much heat to produce, rather than just switching it on and off. It can help a boiler run more gently and efficiently, but only if both the boiler and the thermostat support it.

With simple on/off control, the boiler fires at the temperature it is set to, then stops. With OpenTherm, the thermostat can ask for a lower flow temperature when the house is nearly warm, so the boiler modulates rather than cycling on and off. Condensing boilers tend to work best at lower flow temperatures.

Not every boiler supports OpenTherm, and some manufacturers use their own systems instead. Not every thermostat supports it either, and some only do on certain models or with an extra part. Check both before you choose. If your boiler doesn't support it, on/off control still works fine.

Can I use a smart thermostat with a heat pump or electric heating?

Sometimes, but check carefully first. Heat pumps and electric heating work differently from gas boilers, and the wrong control can make them cost more to run.

Heat pumps work best running steadily at a low flow temperature. A thermostat that switches them on and off like a boiler can reduce efficiency. Many heat pump manufacturers supply or recommend their own controls, so speak to whoever installed the heat pump before adding anything.

Electric heating varies. Modern panel heaters and electric radiators often have their own smart controls built in or as an add-on. Electric underfloor heating needs a thermostat rated for the load, with a floor sensor. Storage heaters are controlled differently again, usually by their own charge settings and your tariff.

Do I need smart radiator valves or zoning?

Only if you want different temperatures in different rooms. A single smart thermostat controls the whole house from one spot; smart radiator valves (smart TRVs) let each room have its own schedule.

Zoning helps in homes where some rooms are rarely used, such as spare bedrooms, or where one room is always too hot or too cold. Several ranges offer smart radiator valves, for example Drayton Wiser, Honeywell evohome, tado and Hive. Check what each range sells now, and whether its valves fit your radiators. Many use a standard thread, but adaptors are often needed.

The room with the main thermostat normally shouldn't also have a standard TRV, as the two can fight each other. Your boiler also needs a path for water to flow when most valves are closed, usually a bypass or a radiator without a TRV. An installer should check this.

Can a smart thermostat control my hot water?

If you have a hot water cylinder, many can, but not all. Look for a model sold with hot water control, sometimes called a dual-channel or heating and hot water version.

With a combi boiler there is no cylinder to control, so a heating-only model is all you need. With a cylinder, the smart receiver usually replaces your existing programmer and takes over both channels. Some setups use a motorised valve and cylinder thermostat, which stay in place.

How much could a smart thermostat save?

It can help if you use the schedule well, but savings depend on your home and habits. If you already turn the heating down when you go out, the difference may be small. None of the features below can fix poor insulation or draughts.

Schedules

Heating on only at the times you need it.

Geofencing

Uses your phone's location to turn heating down when everyone leaves.

App control

Turn heating off from anywhere if plans change.

Room-by-room control

Smart TRVs stop you heating empty rooms.

Open window detection

Some models pause heating when a room cools quickly.

Which smart thermostat should I choose?

Start from your heating system and how you live, then pick a model that fits. Hive, Nest, tado, Drayton Wiser and Honeywell evohome are all common examples; none is the best choice for everyone.

If you have a combi and want simple control

Choose a single-zone thermostat with a good app and schedules.

If you have a hot water cylinder

Choose a model with built-in hot water control.

If your boiler supports OpenTherm

Choose a thermostat that supports it on your model.

If rooms are used differently

Choose a range with smart radiator valves.

If you have a heat pump

Ask the heat pump installer or manufacturer first.

If you rent the home out

Choose something simple that works without the app.

How is a smart thermostat installed, and who can fit it?

There are two common installs: replacing an existing wired thermostat on the wall, or adding a receiver at the boiler or programmer. Both are control wiring jobs, and often both are done on the same visit.

Replacing a wired thermostat is usually the simpler job, as the cable is already there. Adding a receiver means connecting it to the boiler's control circuit, often where the old programmer was. Either way, the wiring may be mains voltage, so it should be done by someone competent, with the power isolated.

We only do the low-voltage or mains control wiring for the thermostat and receiver. Any work on the gas boiler itself, its gas supply or its settings needs a Gas Safe registered engineer. On some boilers, the control terminals sit behind the boiler's casing.

Send photos of your current thermostat, any programmer and the boiler's control panel. We will tell you if it looks like a straightforward fit and give one fixed price before any work starts.