Large boiler, small .......

[D_Hailsham]

Which is master and which is slave on the OpenTherm protocol?

It's all in the Protocol!

4.3.1 Overview
OpenTherm data transfer consists of a series of ‘conversations’ between the devices controlled by a strict
master/slave relationship. OpenTherm requires that the control device, e.g. a room unit, is always the master
and the control plant, e.g. a boiler, is always the slave.

The master issues instructions to, or requests information from, the slave. The slave complies with the instructions or supplies the information.

The main instruction is to tell the boiler (slave) the desired flow temperature. The slave does not need to know how the master arrived at this temperature; and the master does not need to know how the boiler controls the temperature.

 

[bernardgreen]

OpenTherm requires that the control device, e.g. a room unit, is always the master
and the control plant, e.g. a boiler, is always the slave.

Fine...... I can accept that, it is after all the functionality of the over all system.

The electrical configuration of the boiler as slave is I guess necessary to allow a simple thermostat with On-Off control to be used to control a boiler fitted only with OpenTherm interfacing.