What is OpenTherm?

Wikipedia: OpenTherm (OT) is a standard communications protocol used in central heating systems for the communication between a central heating boiler and a thermostatic controller.

As a standard, OpenTherm is independent of any single manufacturer. A controller from manufacturer A can in principle be used to control a boiler from manufacturer B. However, OpenTherm controllers and boilers do not in fact always work properly together. The OpenTherm standard comprises a number of optional features and some devices may include manufacturer-specific features. The presence or absence of such features may impair compatibility with other OpenTherm devices.

OpenTherm History?

OpenTherm was originally created by Honeywell and was sold to the OpenTherm Association on November 1996 for one British Pound. This was no doubt to make the standard independent of any manufacturer.

Modulating Control

Unlike room thermostats that simply tell the boiler when to turn on and off (non modulating graph below) , a modulating control (see modulating graph below) tells the boiler the exact target / set point temperature that is required to be achieved. So as the current temperature starts getting closer to the set point temperature, the boiler starts reducing the flow temperature to match the required demand.

Non modulating thermostat

Modulating Thermostat Graph

OpenTherm Advanced setups

OpenTherm is easier to use on combi boilers. The reason for this is that there is no hot water cylinder to worry about heating to the correct temperatures as required by legionalla prevention(recommended 60 degrees) as OpenTherm can reduce flow temperatures. So on system and regular boilers that have opentherm, in order to also work with hot water cylinders, cylinder temperature reporting must be present in some form. This allows the OpenTherm to fire at high temperature just for the hot water. Note is is advised that in this setup there is priority to the hot water system, otherwise higher temperatures may reach the radiators when you don’t want them to.

Further Resources

If you are looking for OpenTherm Compatible Boilers then go to : https://uk.myboiler.com/opentherm-capable-boilers/

If you are looking for OpenTherm Compatible Controls then go to: https://uk.myboiler.com/opentherm-compatible-controls/

If you need more information regarding OpenTherm, then go to: https://www.opentherm.eu/

Disclaimer: Information on this website is provided for informational purpose therefore we cannot accept liability for subsequent problems. All repair tasks should be carried out by qualified trades people. We may also receive commission payments when you are taken to external websites and complete purchases from third party sellers, once you leave our site, we cannot be held liable for your purchases.