Thermostats: a complete guide

How to choose between smart and traditional thermostats

Thermostats are the control centre of any heating system. For installers, they are not just an accessory but a vital component that determines system performance, comfort levels and customer satisfaction. Choosing between smart and traditional models involves much more than price: it requires understanding compatibility with heating systems, customer expectations, regulatory requirements and opportunities for future upgrades

In this guide, we provide a detailed overview of thermostat types, installation considerations, upgrade triggers and best practices. With insights tailored to heating professionals, the aim is to support installers in making informed recommendations, avoiding costly mistakes, and delivering systems that are efficient, compliant and easy to maintain.

[Table of Contents]

• Types of thermostats and how they work
• Where to install thermostats and TRVs
• Smart thermostat installation: what to consider
• When to recommend a thermostat upgrade
• Installer checklist for selecting and fitting thermostats

Types of thermostats and how they work

A thermostat regulates heating by measuring room temperature and sending signals to the boiler, heat pump or valves. Each model type differs in accuracy, control options and installation complexity. For installers, understanding these distinctions ensures the right device is chosen for each project.

Mechanical thermostats

Mechanical thermostats rely on basic technology such as a bi-metallic strip or liquid-filled sensor that expands or contracts with temperature changes. They switch the heating system on or off once a set threshold is reached.

• Advantages: low cost, long lifespan, reliable in simple systems.
• Limitations: narrow control range, poor accuracy (±2°C), no scheduling or zoning.

Installers still encounter them in older homes or with customers who prefer straightforward, manual control. However, as energy optimisation becomes more important, these models are increasingly replaced with programmable or smart alternatives.

Digital programmable thermostats

Digital thermostats bring greater accuracy thanks to electronic sensors and offer scheduling options, allowing users to set heating programmes for different times of day.

For installers, programmable models are often the “bridge” solution for customers who want improved efficiency without committing to a fully connected system. They are easy to retrofit, require minimal wiring changes, and can reduce customer complaints by providing more stable room temperatures.

Smart thermostats (with app or remote control)

Smart thermostats integrate Wi-Fi connectivity, allowing control via smartphone apps, voice assistants or cloud platforms. Examples include the T6R-HW (single or twin-heating and hot water zone smart control) and evohome (multizone zoning system).

Benefits for installers:

• Faster commissioning with guided setup.
• Remote diagnostics to reduce call-backs.
• Easier upselling opportunities with energy optimisation features.

Smart thermostats also allow installers to position themselves as solution providers, not just product fitters, since they directly influence how customers experience comfort at home.

TRVs and zone-based control systems

Thermostatic Radiator Valves (TRVs) regulate the output of individual radiators. Basic TRVs are mechanical, but programmable electronic versions (such as HR92 with evohome) provide precise scheduling and zoning per room.

From 2027, EU legislation requires programmable TRVs in all buildings with radiators. Installers can use this regulatory change as a strong argument to encourage upgrades. When combined with wall thermostats, TRVs offer the most efficient way to control multi-room comfort.

Read more: TRV replacement: when, how and why to upgrade radiator valves.

Where to install thermostats and TRVs

Correct placement is as important as the device itself. Poorly positioned thermostats often lead to misreadings, wasted energy and frustrated customers.

Thermostat on radiator vs wall-mounted thermostats

Wall-mounted thermostats should be installed about 1.5m above floor level in a room that represents the home’s average usage, usually the living room. They should not be placed near radiators, windows, direct sunlight or appliances.

Some homeowners mistakenly assume that a thermostat works best near a radiator. Installers can explain that this causes inaccurate readings, leading to overheating or underheating. In such cases, TRVs should be used on radiators while the wall thermostat manages overall system control.

TRVs and zoning for individual rooms

TRVs give customers room-by-room control. For example:

• bedrooms can be set cooler at night.
• living rooms can be warmed in the evening.
• spare rooms can be kept at a lower baseline temperature.

This flexibility helps customers reduce energy waste and installers to upsell solutions that meet real comfort needs.

Thermostat for boiler heating systems

In boiler-based systems, the thermostat must accurately reflect the home’s thermal environment. Incorrect positioning can cause the boiler to short-cycle, leading to increased wear and reduced efficiency.

Read more: How to match the right thermostat to each heating system.

Smart thermostat installation: what to consider

Smart controls require a different approach from traditional thermostats. A successful installation depends on preparation, compatibility checks and customer handover.

Benefits for the installer: speed, support, lower call-backs

Smart thermostats often include intuitive commissioning steps. For instance, Resideo’s T6R-HW guides the installer through system type selection, wiring and Wi-Fi setup. By reducing setup errors, installers save time and limit costly return visits.

Common installation mistakes and how to avoid them

• Incorrect wiring: always confirm system type (combi boiler, open vented, heat pump).
• Poor Wi-Fi signal: check connectivity before wall-mounting.
• Placement errors: avoid draughts, direct heat and enclosed spaces.
• Incomplete customer handover: always walk the homeowner through app setup.

evohome and T6R-HW: Resideo solutions that work well with heat pumps

Heat pumps are becoming central to UK energy strategy. Unlike traditional boilers, they benefit significantly from precise control.

• T6R-HW: ideal for single or twin-zone systems with heat pumps.
• evohome: provides multizone control and integrates seamlessly with smart TRVs like HR92.

Installers can highlight to customers that smart thermostats work well with heat pumps without overpromising absolute efficiency gains.

Read more: Installing a smart thermostat: step-by-step for UK systems.

When to recommend a thermostat upgrade

Knowing when to suggest an upgrade is a valuable skill for installers. It helps customers improve comfort and positions the installer as a trusted advisor.

Signs that the current thermostat is inefficient or outdated

• Inconsistent room temperatures.
• No scheduling functions.
• Boiler cycles on/off too frequently.
• Customer complaints about high bills despite unchanged usage.

Pairing smart thermostats with existing heating systems

Even older boilers can often support smart thermostats if wiring is correct. For hybrid systems or heat pumps, evohome offers advanced zoning to match system performance.

Energy optimisation and comfort arguments to support the upsell

Rather than making absolute claims about savings, installers should explain that smart controls help optimise energy use by adjusting heating based on occupancy and scheduling. Highlighting comfort improvements – such as pre-heating rooms before arrival – often resonates more strongly with homeowners.

Installer checklist for selecting and fitting thermostats

Before completing the job, verify:

• system type and thermostat compatibility confirmed.
• correct thermostat location.
• TRVs installed where zoning is required.
• wiring and Wi-Fi tested.
• homeowner trained on use and app setup.
• documentation provided for future reference.

Growing your business with thermostat expertise

Thermostats are no longer just on/off switches – they are the key to efficient, compliant and customer-friendly heating systems. By mastering both smart and traditional options, installers can future-proof their services, reduce call-backs and strengthen relationships with clients.

Discover more on Resideo Academy.
Explore solutions for thermostats and radiator valves: Resideo Comfort Products.