Help! Wrong temperature reported by zone

Stupid, but I allowed the batteries on one of the rads in a multi-room zone to run flat. Somehow this unit now appears to have taken control over the entire zone that is supposed to be monitored by a central placed Round thermostat, so now the HR92 units are all showing 16⁰C whereas the Round is showing 18.5⁰.

Any pointers how I can restore this?