Recommend as follows:
1. Please replace the battery on the transmitter
2. Do the relearning / re-pair the RF once again and see if it works.
If it does not , please contact Siemens by click Contact:
http://www.buildingtechnologies.siemens.com/bt/global/en/buildingautomation-hvac/hvac-products/room-thermostats/autonomous-room-thermostats/heating-cooling/Pages/heating-cooling.aspx
Miri
August 2013