When upgrading to smart heating, it’s easy to get confused by the terminology. You’ll see smart thermostats and smart thermostatic radiator valves (TRVs) mentioned, often in the same breath. This leads to a crucial question: are they two parts of the same system, or competing options? And more importantly, do you need to buy both to get the promised benefits of lower bills and perfect comfort?

The simple answer is that they perform two very different, but complementary, jobs. A smart thermostat acts as the central brain of your heating, while smart TRVs act as the local guards for each room. Using just one gives you some benefits, but using them together unlocks the full potential of a truly intelligent, room-by-room heating system. This guide will explain what each component does on its own, how they combine to create a powerful multi-zone system, and which setup is right for your home. For a full breakdown of the best systems on the market, see our [Smart Thermostats & Radiator Valves in the UK: Complete 2025 Buying Guide].

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The Central Brain: What a Smart Thermostat Does on Its Own

 

A smart thermostat is the master controller of your heating system. It replaces the traditional thermostat on your wall and communicates wirelessly with a receiver connected to your boiler. Its core job is simple: to measure the temperature in its immediate location and tell the boiler to turn on or off to maintain the target temperature for the entire house.

The "smart" part comes from its extra features. You can control it from your phone, set detailed schedules, and use clever functions like geofencing, which automatically turns the heating down when you leave the house.

 

One Sensor, One Zone

The most critical thing to understand about a smart thermostat on its own is that it creates a single heating zone. It only knows the temperature of the room it's in—usually a hallway or living room. If that room reaches your target of 20°C, the thermostat tells the boiler to switch off, regardless of whether the bedroom upstairs is 16°C or the home office is 22°C. Every radiator in your home is either on or off together, based on the reading from one single point.

 

The Problem with Single-Zone Control in Most Homes

For a small flat or an open-plan home, a single-zone system can work perfectly well. However, in a typical UK house with multiple rooms, this approach is often inefficient.

Imagine the thermostat is in your living room, which gets warm quickly due to sunshine or having several people in it. It hits 20°C and switches the boiler off, even though your north-facing home office remains chilly. To warm up the office, you'd have to crank the main thermostat up to 23°C, making the living room uncomfortably hot and wasting energy. This is the fundamental trade-off of a single-zone system and the exact issue that systems like the Google Nest face when compared to multi-zone alternatives. To see how this plays out with real products, read our [Google Nest vs Drayton Wiser: A Head-to-Head Comparison].

 

The Local Guards: What Smart TRVs Do on Their Own

If a smart thermostat is the central brain, smart TRVs are the intelligent gatekeepers on each radiator. These battery-powered heads replace your existing manual or thermostatic radiator valves. Each one contains a small motor and a temperature sensor, allowing you to set a specific target temperature and schedule for each individual room directly from a smartphone app.

 

Individual Radiator Control

On their own, smart TRVs give you precise negative control. When your main heating is on, you can program the smart TRV in the spare bedroom to stay shut, preventing that radiator from heating an empty room. You can set the living room radiator to be 21°C while the bedroom is set to a cooler 18°C. This is a big step up from manual TRVs, as it's all automated via schedules you set in an app.

 

The Key Limitation: They Can't Turn the Boiler On

Here is the crucial drawback of using smart TRVs without a linked smart thermostat: they can only turn radiators off, they cannot turn the boiler on.

If your main heating timer switches the boiler off at 10 pm, the TRVs become useless. Even if your bedroom TRV is set to 19°C and the room temperature drops to 16°C, it has no way to command the boiler to fire up and send hot water. It can only sit and wait for the main system to be switched on again. Think of it like having individual light switches in every room, but the main circuit breaker for the house is off.

 

The Power of Teamwork: How a Combined System Unlocks True Smart Heating

This is where combining a smart thermostat with smart TRVs transforms your heating from a blunt instrument into a precision tool. When the components are from the same system (like Drayton Wiser or Tado°), they talk to each other, creating a true, demand-led multi-zone system. The TRVs are no longer just passive guards; they become active messengers.

 

The "Call for Heat" Concept Explained

The magic of a combined system lies in a feature often called "call for heat" or "heat on demand". Here’s how it works:

1. A Room Gets Cold: Your home office smart TRV detects the temperature has dropped to 17°C, but its target schedule is 20°C.
2. The TRV Sends a Signal: Instead of just waiting, the TRV wirelessly sends a message to the central smart thermostat, effectively saying, "I need heat in the office!"
3. The Thermostat Commands the Boiler: The smart thermostat receives this "call for heat" and instructs the boiler receiver to switch the boiler on.
4. Heat is Distributed Intelligently: Hot water flows through the pipes. The TRV in the office stays open to warm the radiator. Meanwhile, the TRVs in the living room and spare bedroom, which are already at their target temperatures, close themselves off.
5. Efficiency is Maximised: The boiler runs just long enough to heat the specific room that asked for it, without overheating other parts of the house.

This process turns your heating system on its head. Instead of the hallway thermostat dictating the temperature for the entire house, any room can now independently trigger the heating precisely when it needs it.

 

 

Benefit 1: Room-by-Room Comfort on Demand

The most immediate advantage of a combined system is superior comfort. No more cold spots or overheated rooms. You can have your home office perfectly warm at 21°C for the working day, while the rest of the house ticks over at a low 16°C. An hour before you finish work, the living room and kids' bedrooms can automatically start warming up to a comfortable temperature, ready for the evening. Each room is treated as its own independent zone, perfectly matching your family's lifestyle.

 

Benefit 2: Significant Energy and Cost Savings

This room-by-room control is the single biggest driver of savings in a smart heating system. A traditional single-zone system often wastes a huge amount of energy by heating empty rooms. By installing smart TRVs and creating a multi-zone system, you heat only the space you are using, to the temperature you need, exactly when you need it.

Instead of heating the entire three-bedroom house just to keep the living room warm in the evening, you are only heating one or two rooms. This targeted approach means the boiler runs for shorter periods and less frequently, directly reducing your gas consumption. This is the primary mechanism behind [How Smart Heating Actually Saves Money (and Is It Worth It?)].

 

How Integrated Systems Work (e.g., Drayton Wiser, Tado°)

Leading multi-zone systems like Drayton Wiser and Tado° are designed from the ground up for this kind of teamwork. Their starter kits typically include a smart thermostat and an internet hub. You then add their smart TRVs to build out your system. Within their apps, you create schedules for each TRV (or "room"), and the system seamlessly manages the "call for heat" process in the background. You don't need to do anything complex; you just tell the app what temperature you want each room to be and when, and the system figures out the rest.

 

Which Setup Do You Need? Scenarios & Recommendations

The right choice depends entirely on your home and your goals.

 

Choose a Smart Thermostat ONLY If...

• You live in a small, open-plan flat or studio. In this scenario, one sensor is usually enough to accurately manage the temperature of the entire space.
• You have underfloor heating. Most wet underfloor heating systems operate as a single large zone, making a dedicated smart thermostat the perfect controller.
• Your budget is very tight. A starter smart thermostat is cheaper than a full multi-room kit and still provides valuable remote control and scheduling benefits over a basic timer.

 

Choose a Combined System If...

• You live in a typical UK house with multiple rooms and radiators. This is the key use case. You will only unlock significant savings and room-by-room comfort with a multi-zone setup.
• You have rooms that are frequently empty. Spare bedrooms, dining rooms, or even a whole floor can be kept at a low frost-protection temperature until they're needed.
• Different family members prefer different temperatures. You can end the thermostat wars by giving everyone control over their own space (within reason!).
• You work from home. Heating only your home office during the day instead of the entire house can lead to substantial savings.

 

Can I Start with Just Smart TRVs?

Technically, some brands offer TRV-only starter kits (like the TP-Link Kasa KE100). However, as explained, these kits cannot turn your boiler on. They are best seen as a budget way to stop radiators from getting unnecessarily hot when your main heating is already scheduled to be on. For a truly smart and responsive system, you need the link to a smart thermostat.

 

Frequently Asked Questions (FAQs)

 

Can you use any smart TRV with any smart thermostat?

No. To get the crucial "call for heat" functionality, the smart TRVs and the smart thermostat must be from the same brand and designed to work as an integrated system (e.g., Tado° TRVs with a Tado° Thermostat). They use proprietary wireless signals to communicate, so you cannot mix and match components from different manufacturers.

Can smart TRVs turn the boiler on by themselves?

On their own, no. A smart TRV's primary job is to open or close the valve on a radiator. It has no direct connection to the boiler. It needs to be paired with its system's smart thermostat, which acts as the bridge to tell the boiler when to fire up.

Is it worth putting smart TRVs on every radiator?

For most homes, it's beneficial to put them on radiators in all main living areas and bedrooms. However, it's common practice to leave one radiator without a TRV (or with a manual one set to max), usually in a bathroom or hallway. This acts as a bypass, ensuring there is always a path for water to flow if all the smart TRVs happen to close at once, which can protect your boiler's pump.

How much more efficient is a multi-zone system?

The savings can be significant, as you are eliminating the waste of heating empty rooms. Manufacturers quote notable potential savings; for instance, Drayton Wiser suggests savings of up to 19% can be achieved with a full multi-room system. However, the exact amount you save depends entirely on your previous heating habits, your home's insulation, and how you schedule your new zones.

 

Internal Links Included

• Smart Thermostats & Radiator Valves in the UK: Complete 2025 Buying Guide

• Google Nest vs Drayton Wiser: A Head-to-Head Comparison

• How Smart Heating Actually Saves Money (and Is It Worth It?)