Honeywell AQ25A Series Technical Reference Booklet page 203

Minimum Setpoint Temperature
This parameter is the minimum temperature at which the thermostat
can be set.
Maximum Setpoint Temperature
This parameter is the maximum temperature at which the thermostat
can be set.
Freeze Protection Temperature
This parameter is used to prevent frozen pipes inside the room where
the thermostat is located. When the Freeze Protection mode is acti-
vated by the hydronic zoning controller, the thermostat is placed at
the Freeze Protection temperature.
10 69-2005EF