OpenTherm was founded in 1996 because multiple manufacturers needed a simple-to-use communicating system between room controller and boiler.
Furthermore, the Association is also active in lobbying for the interests of its members and is also present at exhibitions like the ISH (Frankfurt) and the Mostra Convegno (Milan).
Whilst OpenTherm is a point-to-point connection, an extra device (gateway) is added between the primary and the secondary.
The sequencer includes additional software to increase or decrease the number of running boilers to match the actual heat demand.
The sequencer also needs a sensor to measure the temperature of the combined output from the boilers and usually would also control a main circulation pump.
The controller transmits to the boiler by sending a Manchester-encoded sequence in the Voltage domain.
The data in the communication packet is functionally specified and is called OpenTherm-ID (OT-ID).
(OT specification v3.0) When OT/- is used the primary generates a PWM voltage signal, representing the boiler water temperature set point.
With this primary manufacturers can add more functionality to their products (backlight or extra sensors).
By handing over the test report and a Declaration of Conformity to the association, the manufacturer is allowed to use the OpenTherm logo.