What Is OpenTherm? Everything You Need To Know

James Elston
Written by James Elston
Updated on 17th May 2024
Posted on 15th May 2024
Topic: Boiler Advice
What is OpenTherm Everything You Need To Know

Living in the UK, there is no doubt you’ve heard of OpenTherm. But what does it actually mean? 

opentherm logo

We’re taking you through everything you need to know, including what OpenTherm is, how it works, and its benefits. 

So, if you’re ready to start saving money and the planet at the same time, let’s get into it. 

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What Is OpenTherm?

In its most basic form, OpenTherm is the language that connects your thermostat and boiler at all times. This is what gives your boiler the information it needs about room temperature so that it can run smoothly.

Today’s heating systems are usually modulating. This means that your boiler can run at a lower or higher wattage depending on what’s happening with the boiler’s water temperature.

Basically, your modulating boiler heating system detects how much energy it’s going to need to warm water in the house based on the water it’s getting and the room temperature you require.

The OpenTherm heating system allows your thermostat to communicate this need to the boiler.

Rather than the boiler running at full capacity, the message from the thermostat allows your heating system to modulate the water temperature you need.

How Does OpenTherm Work? 

Let’s start with an example. If you walk into your home after a holiday and it’s 0 degrees, you’re going to want the room temperature up pretty quickly. 

What about a lovely 22°C? 

Getting central heating systems to that point takes a serious amount of heat. So, off the thermostat goes to tell the boiler to make the radiators hot. 

Now, before things like OpenTherm your radiator would remain at 22°C until the entire room was at that temperature.

Most heating controls worked with a simple on/off switch. Which worked as follows:

  • Switch on.
  • Heat up.
  • Switch off when the water temperature reaches the required heat.
  • Switch back on to reheat when it cools down.

The constant on/off uses a lot of energy to get going every time it needs to heat up.

This is where OpenTherm comes in. It allows the heating controls of the thermostat to tell the boiler that the room is nearly at the ideal temperature and it’s a good idea to slow down. The boiler then reduces output, keeping the room at the desired temperature without constantly reheating from the start.  

The boiler and thermostat work together through OpenTherm to keep your home cosy much more efficiently. 

The days of feeling stuffy every hour are over. Your radiators won’t be pumping heat in like they used to. 

However, while this all sounds great, only certain boilers work with OpenTherm. This means you might be stuck with the traditional heating system until you get a modern boiler.

Not quite sure about OpenTherm? Why not consider a smart thermostat instead which you can control your boiler with your phone?

How Does OpenTherm Save Energy?

Since your boiler is modulating it uses less fuel than traditional boilers. These need a lot of power to turn on and off every time the water temperature goes down. 

By using less fuel, carbon emissions reduce considerably. In fact, studies show OpenTherm heating systems could reduce your emissions by as much as 15%. 

But the good news doesn’t end there. OpenTherm can work with most modern low-carbon heating systems. 

The Benefits Of OpenTherm

Switching to an OpenTherm heating system is a big change if you’re used to how old boilers work. However, there are many great benefits, including:

  • Perfect room temperature: Your home won’t be too hot or too cold. OpenTherm keeps things much more regulated. 
  • Easier to fix: A heating engineer can use their phone to assess any issues without having to come to your home. This is a big plus for saving on call-out fees and even reduces carbon emissions because the need to travel isn’t there. 
  • Few replacements: Modern boilers and thermostats are much more durable than ever before. Also, because your boiler isn’t switching on and off all the time the chance of an issue is reduced.  
  • Monitor your boiler: You can check how your boiler is performing straight from your phone. So, you may not even need a heating engineer. Some apps will tell you when there’s an issue. 
  • Money saver: Since you’re using less fuel, your overall heating bills will be significantly less. 
  • Energy efficiency: Using less fuel is much better for the planet. We need fuel. There isn’t a way around it, but by using less you can make a big difference to your overall eco-footprint. 


How do I know if I have OpenTherm?

The best way to check is to look for the OpenTherm logo on your boiler and room thermostat. Generally, most modern boilers are OpenTherm compatible. 

Can any company use OpenTherm?

Yes, OpenTherm is an open communication protocol for heating controls. It is not owned by a single company or organization. Any company can use OpenTherm protocols for their products. There isn’t a specific OpenTherm boiler, it’s open to all.

Can I use OpenTherm with my smart home systems?

Yes, OpenTherm has an app that integrates seamlessly with smart home systems. You can access your OpenTherm info from your chosen interface. 

Wrap Up

OpenTherm is the way of the future. It’s taken a system we’ve used for decades and changed things slightly to keep up with the growing need for us to be more eco-conscious. If you choose one of our speacial offer upgrades, you can get OpenTherm with our EPH CP4i thermostat.

It also genuinely helps from a money point of view with the cost of living crisis going nowhere quickly. 

While it is a big change, OpenTherm is convenient, cheaper, and better for the planet. We can’t really find a reason not to make the change. 

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 15th May 2024
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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