What is OpenTherm? How can it help you save money? And how do you know if your boiler has it?

In order to modify the temperature flow via a heating system, heating controls and the boiler communicate using the OpenTherm protocol.

This can help a heating system use less energy while still keeping the house’s temperature at the desired set point.

Numerous boilers and smart thermostats communicate using the OpenTherm language.

Your home will be cosier than ever with a modulating boiler and thermostat that both speak OpenTherm.

Although Honeywell created the OpenTherm language, any boiler or thermostat manufacturer can use it.

Although OpenTherm has been available for a while—heating systems all around Europe have been utilizing it— the UK has lagged a bit in adoption.

Learn all about the different types of boilers, including condensing boilers, LPG boilers, oil boilers, Opentherm boilers and calculating boiler size in our guide.

Benefits of OpenTherm Boilers

Below are some of the advantages of OpenTherm boilers:

• The significant advantage of OpenTherm is its energy efficiency, which helps to reduce fuel costs. By operating at lower flow temperatures for extended periods of time, OpenTherm not only keeps the ideal room temperature set point constant but also improves the boiler’s efficiency. This guarantees the boiler continues condensing for a longer duration.

• The effect on the appliance is less than the case when the boiler was constantly starting and stopping since boilers are kept in condensing “mode” for longer periods of time. This results in less wear and tear, allowing the boiler to run at peak efficiency for a longer period of time. Some OpenTherm heating controls display boiler states and a number of problem codes right on the thermostat’s screen, giving the installer more information.

• The communication of the control set point (heat requirement) to the heating appliance is the most highlighted feature of every OpenTherm controller. The sensor controls this component using either another type of control, such as outside temperature control, or the gap between the set temperature and the favourable temperature.

How do you know if your boiler is using OpenTherm?

The fastest and most efficient method to learn is to check your boiler for an OpenTherm logo. It’s probably not an OpenTherm boiler if you can’t see one.

To be sure, though, it is worth consulting the instructions or giving the maker a quick call.

How old is your boiler? Should you consider a boiler repair or start looking at the latest boiler prices? It’s no secret that boiler efficiency deteriorates over time.

OpenTherm boilers & branded controls

Opentherm is fully compliant with the boilers listed below. This includes companies like Baxi, Main, Ferroli, Ideal, and Viessmann implementing this technology.

However, not all boiler manufacturers have made their Opentherm boilers compatible with third-party Opentherm controls.

The controls provided are the manufacturer’s own controls, so they should function just fine.

Manufacturer	Baxi	Ferroli	Ideal	Main	Viessmann
Models	600 Combi	iBoiler Combi i29	Logic Combi + C24, C30, C35	Eco Compact Combi 25kW, 30kW	Vitodens 100
400 Combi	Logic Combi C24, C30, C35
200 Combi	Vogue Combi C26, C32, C40
100 Combi
Boiler branded Opentherm controls	uSENSE		Touch Connect
Ideal 204789 Rf wireless programmable room thermostat

The OpenTherm logo serves as a quick way to recognize its goods.

The logo ensures that there will be at least a minimal amount of communication between the room thermostat and the central heating system.

The extra features the manufacturer built in will determine how much involvement there is.

The room thermostat and central heating unit terminal clips are both close to where you may find the logo.

Third-party OpenTherm controls

We can install certain third-party controls that could still communicate intelligently with the boiler because the OpenTherm language is open.

To be fairly obvious, you should refer to boiler controls created by companies other than boiler manufacturers as third-party controls, such as Honeywell Evohome or Google Nest.

The boilers indicated in the table above can all be operated by any of the third-party controls listed below, but this is not necessarily the case in reality.

Not all Opentherm controllers from third parties work perfectly with Opentherm boilers.

Check with the boiler manufacturer to make sure that the third-party control you want to use is completely compatible with their boilers.

Two, of the seven third-party controls, are common programmable room thermostats and five are internet controllers.

Want to learn how to use your boiler better? Read our complete guide on boiler flow temperature, how to optimise your boiler settings and find out how much gas a boiler uses here.

They are all in compliance with Boiler Plus since they all include load compensation controls (Opentherm).

Third Party manufacturers that will work with all Opentherm boilers	Drayton	Nest	Tado	Honeywell	Honeywell	Honeywell	Salus
Model	Wiser (Kit 1, 2 and 3)	Thermostat E	Tado Smart thermostat (with extension kit)	Lyric T6R and T6R-HW	T4R, TRM	Evohome	RT520 + RT520 RF
Base unit/thermostat – suitable combi boilers	£135.00	£199.00	£200.00	£242.00	£127.00	£249.99	£70.00
Additional costs for separate hot water control	NA	Included	Included	Included	No	included	No
Combined costs for heating and hot water	£149.99 Kit 2 – heating and hot water control	£199.00	May require an extension kit – £89.99	£242.00	NA	249.99	NA
Warranty/guarantee	1 year	2 years	2 years	1 year	1 years	1 year	5 years
Heating controls	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Hot water time/boost	Kit 2 model	Yes	Yes (possible extension kit)	Yes	No	Yes	No
Weather compensation, load compensation or smart automation and optimisation	Load compensation and smart automation and optimisation	Load compensation and smart automation and optimisation	Load compensation w/Opentherm boilers and Smart automation and optimisation	Weather and load compensation	Load compensation and weather compensation (T4M)	Load compensation	Load compensation
Works with Smart TRVs	Yes – Drayton Wiser Smart TRV	Yes – Energenie	Yes – Tado Smart TRVs	No	No	Yes	No
TPI software	No	Yes	Yes	‘Fuzzy logic’	‘Fuzzy logic’	Yes	Yes
OpenTherm	No	Yes	Yes	Yes	Yes	Yes	Yes
Boiler Plus compliant for combis?	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Boiler Plus compliant for heat only and system?	Yes	yes	Yes	Yes	Yes	Yes	Yes
Heating zone capabilities	1 (Kit 2 gives 2 channels – 1 heating and 1 hot water)	3 zones with pipework adjustment or more with Energenie smart TRVs	1 heating zone	1 heating zone	1 heating zone	Multiple with additional pipework or via Smart TRVs	1 heating zone
Geo location features	Yes – via IFTTT	Yes	Yes	Yes	No	Yes – via IFTTT	No
compatible boiler types	Combi, heat only and system	Combi, heat only and system	Combi, heat only and system	Combi, heat only and system	Combi, heat only and system	Combi, heat only and system	Combi, heat only and system

Alternatives to OpenTherm

However, that does not mean you cannot install an advanced control on other boiler types or on older boilers.

Keep in mind that only combi boilers are required to be fitted with an advanced control under Boiler Plus.

A brief overview of additional choices for older and non-combi boilers is provided below.

There are two alternatives available to customers installing a new combi boiler:

• The most effective operation of the boiler is achieved by optimisation controls rather than compensatory controls, which change the gas valve. All boilers can use them to increase their efficiency. There are numerous smart controllers from third parties that offer optimization features and are compatible with the overwhelming majority of boilers.

• Six boiler manufacturers create their own internet heating controls that are Boiler Plus compliant and can be used with some of their boiler models. Numerous sophisticated controls are available from size boiler manufacturers with appropriate types of boiler in their line.