A Xenta 121-FC controller setup as a 2 pipe system will not heat or cool even though the terminal load is showing a demand.
The Xenta 121-FC does not have a water temperature sensor wired into the device
For this functionality to work automatically, a water temperature sensor must be wired into the U1 terminal on the FC-121.
The other alternative is to set the supply temperature via the SNVT nviSourceTemp. This can be done from a supervisory system that is feeding the water to the 121-FC.
To use the SNVT nviSourceTemp as a solution the correct heartbeat will be require to be set in the 121-FC.
Here is a link on how to set that up