Thank you for the insight to the system operation. We have 4 dual HR92 zones the bedroom where the problem was being the 4th. What I observe is all the multi zone radiators act independently, yes one may be designated as the master temperature control in a zone, but frequently one radiator is on whilst the other is off, they definitely supply heat independently to meet the overall room demand. I have been monitoring the bedroom closely and even just now checked and the radiator under the window is on and the one the other side of the room is off, the same happened all of yesterday after I had adjusted it. The kitchen and breakfast room does the same, we have a radiator that is close to the heating boiler and that rarely comes on as a member of the kitchen zone.

I think it would be sub-optimal and inefficient for both radiators to be controlled by one sensor but not allow an individual HR92 to switch itself off or reduce heat when it starts to reach the target temperature.