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Last updated: 7th March, 2024


OpenTherm Heating System

OpenTherm Heating System

Key takeaways

  • OpenTherm facilitates advanced communication between boilers and thermostats for improved heating efficiency.
  • The system enables boilers to modulate heating output for precise temperature regulation.
  • It supports integration with smart technology, offering enhanced user control and potential cost savings.

OpenTherm began with the objective of streamlining communications between heating system components.

Heating efficiency and smart technology integration are milestones in the advancement of home heating systems. The OpenTherm heating system embodies these advancements, offering a significant leap in the way boilers and thermostats communicate. 

OpenTherm is not bound to a specific brand, which promotes a versatile approach to heating regulation through a universal language. This system allows thermostats and boilers to exchange information bidirectionally, leading to precise control over the heating output based on real-time temperature readings.

Unlike traditional systems that operate with a simple on/off mechanism, OpenTherm facilitates modulating control. This means that boilers with OpenTherm capabilities can adjust their output to match the actual heat demand more accurately. 

Consequently, this optimises energy usage, reduces emissions and can potentially lower heating costs. Additionally, the system supports the integration of modern condensing boilers with smart thermostats, enhancing user experience with remote control and monitoring.

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Overview of OpenTherm

OpenTherm serves as a modern communication protocol, bridging the gap between boilers and room thermostats. It is a technology standard designed to enhance the efficiency of central heating systems and provide users with advanced control over their home's temperature and energy consumption.

History and Development

OpenTherm began with the objective of streamlining communications between heating system components. With an emphasis on interoperability, the technology has undergone continual refinement. It originated as a multi-brand standard, which now supports various manufacturers' equipment, allowing for seamless integration across different devices.

Principles of OpenTherm Technology

At its core, OpenTherm operates on a sophisticated method of data transfer. It facilitates a two-way dialogue between thermostats and boilers, enabling them to share detailed telemetry. This protocol allows heating appliances to run more efficiently by adjusting to real-time data, rather than simply toggling on and off. The technology spans a range of functionalities, from simple temperature modulation to intricate energy-saving algorithms.

Key Components

The OpenTherm Heating System incorporates advanced communication technology to facilitate efficient interactions between the boiler and thermostat. This synergy is vital for optimising energy usage and maintaining optimal home temperatures.

OpenTherm Controllers

OpenTherm-compatible controllers, commonly referred to as thermostats, are crucial in regulating home heating. These devices allow users to set desired temperatures, which are then communicated to the boiler. Manufacturers of these controllers often display the OpenTherm logo to signify compatibility. It's important that the thermostat chosen is designed to work seamlessly with the specific brand of the boiler, ensuring that the manufacturer's guidelines are followed for optimal performance.

Communication Interface

The interface between the boiler and the thermostat is the cornerstone of the OpenTherm system. This digital communication conduit enables the exchange of precise temperature readings and boiler performance data. The protocol used for this exchange ensures that the boiler operates at varying outputs, which directly corresponds to the real-time heating needs of a space. These modulating signals help in maintaining the efficiency of the heating system, thus potentially lowering energy bills and reducing environmental impact.

In summary, the integration of OpenTherm controllers and a robust communication interface forms the bedrock of an OpenTherm Heating System, ensuring that the system runs efficiently and effectively.

Temperature Regulation

Effective temperature regulation is at the heart of an OpenTherm Heating System, ensuring a balance between comfort and energy efficiency. The system intelligently manages room and water temperatures based upon precise control set points.

Room Temperature Control

OpenTherm greatly enhances room temperature stability by continuously adjusting the boiler's heat output. Through real-time dialogue with the thermostat, the boiler is informed of the current room temperature. If the room temperature deviates from the temperature set point, corrections are made dynamically, thereby maintaining the desired comfort level with pinpoint accuracy.

  • Temperature Set Point: The desired room temperature as set on the thermostat.

  • Control Set Point: The specific temperature the boiler must achieve to maintain the set point.

The system ensures that temperature fluctuations are minimised by managing how frequently and to what degree the boiler operates. The end result is a room that stays consistently at the chosen comfort level without the common peaks and troughs associated with traditional on/off heating systems.

Water Temperature Management

Managing the flow temperatures to radiators and taps is a complex task and OpenTherm simplifies this through continuous modulation. It can adjust the temperature of the water sent into the heating system depending on both the outside temperature and the heat loss within the property. This not only prevents overheating or underheating of spaces but also optimises energy usage and extends boiler life.

  • Flow Temperature: The actual temperature of the water circulating in a heating system.

This direct communication allows the boiler to operate at lower temperatures when less heat is needed, which helps to conserve fuel. Conversely, during colder spells, it increases the water temperature appropriately. By fine-tuning the water flow temperatures, OpenTherm brings about a more efficient use of energy and ensures that the heating system operates within ideal parameters.

System Efficiency

In the realm of heating solutions, the efficiency of an OpenTherm heating system hinges on its ability to optimise energy usage and reduce fuel costs. Modulating boilers and advanced control mechanisms are central to its efficacy.

Energy Savings

With OpenTherm, energy efficiency is significantly enhanced by facilitating precise control over the heating system's operation. This protocol allows the system to adjust the boiler's output to the exact level needed to maintain a consistent temperature. The key advantages include:

  • Load Compensation: The ability of the system to adapt to the actual heating demands in real time, which minimises energy wastage.

  • Weather Compensation: Taking external temperature into account, the system modulates the heating output, ensuring even greater fuel efficiency.

Studies suggest that by maintaining lower flow temperatures over prolonged periods, OpenTherm heating systems can curb emissions by up to 15%.

Modulating Boilers and Control

Modulating boilers play a critical role in OpenTherm's efficiency narrative. These boilers can finely tune the heat output to match the precise requirements of the space being heated, which translates to:

  • Reduced cycle times

  • Less fuel consumption

  • Enhanced longevity of the boiler

The boiler’s efficiency peaks when paired with intelligent controls that command the system's operation, ensuring optimal energy use. This synergy fosters a harmonised environment where energy savings are maximised without compromising on comfort.

Heating System Components

Heating systems are composed of various essential elements, each playing a pivotal role in providing warmth. Integral parts include radiators and pipework for distribution, as well as boilers and thermostats for temperature regulation.

Radiators and Pipework

Radiators serve as the primary means for heat emission into rooms. These flat-panel or columned devices connect through an intricate network of pipes, facilitating the flow of hot water. Pipework adjustment is vital in ensuring the system works at its optimal efficiency. This involves balancing, which evenly distributes water and heat throughout the radiators.

Boilers and Thermostat Types

Boilers, particularly new boiler installations like the condensing boilers, are at the heart of the heating system. These modern boilers adjust their output to match the heat requirement, thus conserving energy.

Thermostats, evolving from simple on/off types to intricate programmable thermostat designs, provide granular control. A programmable room thermostat can schedule heating, ensuring the system's operation aligns with the occupants' lifestyle and reduces wastage. OpenTherm technology facilitates two-way communication between the boiler and the thermostat, further fine-tuning the system's response to actual heating demands.

Smart Technology Integration

In an era where home heating efficiency is paramount, OpenTherm systems leverage smart technology to enhance control and optimisation of domestic heating.

Smart Thermostats and Features

Smart thermostats serve as the nucleus of OpenTherm heating systems. They communicate with the boiler using a specialised protocol to regulate temperature finely. Features of smart thermostats, such as adjustable heating schedules and real-time temperature data, empower homeowners with precise control. Here's what they offer:

  • Remote Adjustability: Adjust temperature from any location.

  • Optimisation: Learn user preferences for efficient heating.

  • Integration: Work with SMART TRVs (Thermostatic Radiator Valves) for per-room temperature control.

Typical setups might feature an Intergas Xclusive 30 or similar OpenTherm-compliant boiler in conjunction with an intelligent thermostat that adjusts the boiler's flame intensity based on real-time data, resulting in energy savings and consistent comfort.

Automation and Internet Control

With automation, OpenTherm systems transcend manual control, employing internet-enabled devices to automate home heating. Internet Control involves:

  • Geo-location Features: Modify heating based on the occupants' location.

  • IFTTT Integration (If This Then That): Create custom 'recipes' that signal the heating system to respond to other smart devices.

Central to this connectivity are smart controls, which allow the user to manage their heating system over the internet, providing convenience and further energy efficiency. Through mobile applications, users can automate behaviors such as turning off the boiler when everyone has left the house, or warming up the bedrooms just before the usual time of arrival. Further integration with services like IFTTT can extend this functionality to interact with other smart home devices, ensuring that the system's response is both adaptive and intuitive.

Installation and Maintenance

A properly installed and maintained OpenTherm Heating System ensures efficient temperature management and longevity of the setup. Attention to detail by a qualified heating engineer is paramount during installation, and regular servicing reduces the risk of wear and tear.

Setting Up an OpenTherm Heating System

When installing an OpenTherm Heating System, the heating engineer must calibrate the boiler and thermostat to communicate effectively—the heart of OpenTherm's functionality. The installation process involves:

  • Connecting the thermostat: The OpenTherm room thermostat must be wired correctly to the boiler to allow two-way communication.

  • Configuring temperature flow settings: The engineer sets up the boiler to modulate its heating output based on real-time data received from the thermostat.

Careful installation ensures the main components—the boiler and thermostat—operate harmoniously, maintaining a comfortable indoor climate without needless energy expenditure.

Servicing and Longevity

Regular maintenance by professionals ensures that an OpenTherm Heating System operates at peak efficiency. Key servicing activities include:

  • Inspection of communication protocols: Technicians check if the boiler and thermostat communication is flawless, which is essential for optimal functioning.

  • Wear and tear assessment: Components are examined for signs of deterioration, which can affect the system's performance.

Frequent servicing not only prolongs the lifespan of the system but also guarantees the maintenance of the desired internal temperature without excessive energy use.

Regulatory and Industry Standards

Key developments in regulatory standards are shaping the landscape for OpenTherm Heating Systems, ensuring efficient operation and compliance with recent mandates.

Boiler Plus Legislation

The Boiler Plus legislation, introduced in the UK in April 2018, is part of the government’s 'Clean Growth Strategy'. Its core focus is on raising the efficiency of heating systems and has directly influenced the integration of thermostat and boiler technologies like OpenTherm. It requires all gas boilers to have a minimum performance standard with a 92% ErP for combi boilers. Additional requirements include the installation of at least one of the following: weather compensation, load compensation, flue gas heat recovery, or smart control featuring automation and optimisation functions.

European Standards and Regulations

On a broader scale, the European Union's regulations, particularly those concerning the Eco-design and Energy labelling standards (ErP Directive), play a significant role in shaping heating system standards. These regulations typically define the minimum efficiency and environmental standards for boilers and heating components sold within Europe. OpenTherm systems need to adhere to these European-wide standards to ensure compatibility and efficiency across borders. This requirement aligns with the wider European Single Market's goal, fostering interoperability and high-performance benchmarks across member states' energy systems.

Compatibility and Interoperability

When integrating an OpenTherm heating system, the synergy between the boiler, thermostat, and additional smart devices is paramount to achieving an efficient and seamless performance.

Manufacturer Compatibility

A quintessential element in the OpenTherm ecosystem is the compatibility between boilers and thermostats. OpenTherm boasts a common language, which is adopted by a variety of manufacturers to ensure their devices can communicate effectively. Notably, Viessmann, Baxi, Ideal, and Ferroli are amongst those who have implemented this protocol into their boilers. However, it's pivotal to acknowledge that some manufacturers, while offering OpenTherm-compatible boilers, may only ensure full functionality with their proprietary controls. Compatibility across different brands may not be implicit and should be verified prior to installation.

  • Fully Compatible Manufacturers:

    • Viessmann

    • Baxi

    • Ferroli

    • Ideal

  • Note on Proprietary Controls: Compatibility might be restricted to manufacturer-specific thermostats.

Smart Device Interconnectivity

In the realm of smart heating controls, the OpenTherm language paves the way for interoperability with a spectrum of smart devices. The protocols allow for consistent and accurate data exchanges that underpin efficient system function. Devices such as the Honeywell range and Vaillant's vSMART integrate seamlessly with OpenTherm-enabled boilers. Additionally, solutions like Worcester's Wave smart thermostat and Nest leverage this communication protocol to enhance heating efficiency. It is critical to inspect each smart device for OpenTherm certification to ensure harmonious operation.

  • Smart Devices Compatible with OpenTherm:

    • Honeywell thermostats

    • Vaillant vSMART

    • Worcester Wave

Each device plays its part in a collective endeavour to provide real-time responsiveness and tailored heating experiences. It's in the user's interest to confirm interoperability to harness the full potential of their OpenTherm-enabled heating system.

Consumer Considerations

When evaluating OpenTherm heating systems, homeowners should weigh financial implications and compatibility factors to make an informed choice.

Costs and Financial Incentives

OpenTherm systems may present an initial investment higher than traditional heating systems, but they often lead to long-term savings on energy bills. Their modulating ability ensures they run at variable and highly efficient outputs, matching the exact heating demand of the home. This specificity not only reduces energy consumption but can also extend the boiler's life expectancy, providing further cost savings.

Considering financial incentives, the UK government occasionally offers schemes to encourage the adoption of more efficient, low-carbon heating systems. Homeowners should explore available options that may offset the initial cost, such as grants or rebates designed to reduce carbon footprints and energy costs.

Choosing the Right System for Your Home

Selecting an OpenTherm system that fits your home requires an understanding of both the technical standard and how it integrates with existing infrastructure. The standard of OpenTherm ensures compatibility between various boilers and thermostats, yet not all manufacturers fully support third-party controls; some restrict to their own proprietary systems.

Here are essential points a potential buyer should consider:

  • Boiler compatibility: Ensure your existing or new boiler is OpenTherm compatible.

  • Control flexibility: Seek systems that allow integration with multiple third-party controls, granting you more choices in system management.

  • Heating requirements: Evaluate if single or multiple zones are needed for your heating and hot water regulation.

By considering the above factors, consumers can select an OpenTherm system that not only provides enhanced efficiency and potential cost savings but also aligns seamlessly with their specific home heating needs.

Advancements in Heating Technology

Emerging smart home innovations are transforming the warmth and efficiency of our living spaces. Key among these advancements is the OpenTherm protocol, a leap forward in digital climate control.

Innovations in OpenTherm Devices

OpenTherm devices are becoming increasingly sophisticated, as manufacturers integrate design ingenuity with digital capacities. Today's systems are not merely on or off; they modulate. They adjust the boiler's output precisely, enhancing comfort and reducing energy wastage.

One pivotal innovation comes in the form of the tado° Smart Thermostat. This technology offers granular control over heating, learning from your habits to optimise temperature and efficiency. It turns the heating down when the last person leaves and warms up the house by the time the first person is about to return.

Honeywell Evohome, another leading name in heating technology, allows for the zoning of heating. This means you can control the heat in different parts of the house independently, tailoring comfort and saving energy where it's not needed. The Evohome's linkage to the OpenTherm protocol has opened avenues for more nuanced temperature control.

Diverse products such as Salus RT520, Hive's Touch Connect, and the Ideal 204789 RF Wireless Programmable Room Thermostat are part of this burgeoning landscape. They bring their design philosophies, marrying user-friendliness with advanced functions.

The Lyric T6R, with its wireless portability, and Salus's iT500, accessed via smartphone, harness the benefits of remote control, ensuring temperatures can be adjusted on the go. Through OpenTherm, these devices offer bespoke heating solutions for modern lifestyles.

Furthermore, Wiser's smart thermostats incorporate multi-zone controls with OpenTherm, allowing for an efficient, demand-based heating system. The compatibility with existing boilers is a testament to OpenTherm's flexible and future-forward approach.

In a field bristling with competition and variety, each new model—from tado° to Honeywell’s Evohome—bears witness to constant innovation. Design and technology fuse in these thermostats, bringing forth a more intuitive and energy-conscious future for home heating systems.

Best Boiler Brands: Vaillant, Viessmann, Alpha, Ideal, Worcester Bosch

Selecting the right boiler brand is pivotal for ensuring efficiency, reliability, and longevity in home heating. Among the myriad of options, brands like Vaillant, Viessmann, Alpha, Ideal, and Worcester Bosch distinguish themselves with innovative technology and customer satisfaction. Below is an in-depth comparison of these brands, focusing on their standout models and unique industry positions.

Comparative Analysis of Standout Models


Standout Model

Energy Efficiency

Unique Features

Environmental Impact


ecoTEC Plus


Eco-friendly, quiet operation

Reduced carbon emissions


Vitodens 100-W


Compact design, smart compatibility

Low emissions technology


E-Tec Plus

High efficiency

Compact, cost-effective

Energy-saving operation


Logic Plus


User-friendly, easy installation

Efficient energy use

Worcester Bosch

Greenstar i


Robust build, smart controls

Eco-conscious design


Vaillant's eco-friendly ethos shines in their ecoTEC range, particularly the ecoTEC Plus and ecoTEC Exclusive models. These boast top-tier energy efficiency and reduced carbon footprints. They're known for quiet operation and user-friendly controls, making them a harmonious blend of performance and environmental responsibility.


Viessmann's Vitodens series, especially the 100-W and 200-W, are hallmarks of high-efficiency and technology. These models feature compact designs and stainless steel Inox-Radial heat exchangers for durability. Advanced features like smart thermostat compatibility offer enhanced control and user convenience.


Alpha Heating Innovation's E-Tec range, particularly the E-Tec Plus, offers a fine balance between affordability and quality. Notable for their impressive energy efficiency and compact size, these boilers are suitable for various home types, making them an ideal choice for straightforward, efficient heating solutions.


Ideal Boilers, especially the Logic Plus range, are lauded for their reliability and value. These boilers stand out with their efficiency, user-friendly interface, and compactness, favoured for their ease of installation and maintenance. They come with comprehensive warranties, offering peace of mind and reliability.

Worcester Bosch

A leader in the market, Worcester Bosch is synonymous with quality and reliability. The Greenstar range, including models like Greenstar i, Si, and CDi, is known for its efficiency and robust build quality. These boilers blend innovative features such as smart thermostat compatibility with user-friendly controls, making them a top choice in many homes.

iHeat New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Effectively, new boiler cost can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


Get a quote

System to combi conversion


Get a quote

New boiler install


Get a quote

Back boiler to a combi


Get a quote

System to system


Get a quote

Frequently Asked Questions

Can you convert a boiler to OpenTherm?

Converting a non-OpenTherm boiler to work with OpenTherm controls is not straightforward. It relies on the boiler’s design and whether the manufacturer supports such a conversion. In many cases, a conversion kit or an adaptor from the boiler manufacturer may be necessary.

Which boilers use OpenTherm?

Many modern condensing boilers are designed to use OpenTherm, particularly those that modulate their output for increased efficiency. It’s important to check with the boiler manufacturer or refer to the boiler's specifications to ascertain OpenTherm compatibility.

How do I know if my boiler has OpenTherm?

To determine if a boiler supports OpenTherm, one should consult the boiler's user manual or specifications. Alternatively, contacting the manufacturer or a qualified heating engineer can provide a definitive answer.

Can I set a maximum boiler temperature with OpenTherm?

Yes, with OpenTherm, it's possible to set a maximum boiler temperature. This allows better control over the heating system, helping maintain efficiency and comfort within the property.

How much difference does OpenTherm make?

OpenTherm can make a significant difference in how a heating system operates. By allowing precise control of the boiler based on real-time data, it ensures that heating is delivered more efficiently and with better modulation to match the property's requirements.

How much more efficient is OpenTherm?

The exact efficiency gains from OpenTherm will vary depending on the existing heating system, the property, and how the system is used. However, due to its ability to modulate the boiler's operation precisely, OpenTherm can lead to better energy efficiency and reduced heating costs over time.

What is the difference between on/off and OpenTherm?

An on/off control system simply turns the boiler on when heating is needed and off when it isn’t, which can lead to larger temperature fluctuations and potentially less efficient operation. OpenTherm, however, communicates detailed temperature data, allowing the boiler to modulate and run at varying outputs, which enhances efficiency and temperature stability.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.