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 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.
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.
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/