Upon clicking the 'Set all rooms to default' button your settings will not be written to the rooms.
We are aware of an issue with the 'Set all rooms to default' option and our developers are making improvements to this.
In the meantime the Workflow is as follows:
1. Select the zone for which you wish to specify Defaults:
2. Change the figures and settings as required.
3. Click on Select Rooms. Select each room in turn. (At this stage you should check that correct HVAC is specified under Room uses HVAC). Clicking on the Use Default tickbox will then apply your Default settings to the Room selected.