HydroStat User Guide

7
The HydroStat IC is equipped with a second zone for use with a 120 volt circulator. Unless the control is
factory installed on a boiler designed for primary/secondary heating loops, the zone will be set to function
with an indirect water heater for domestic hot water (DHW). The T-T input for this zone is the small screw
terminals labeled "DHW or Zone2". The zone output is located in the LINE VOLTAGE plug receptacle (see
page 3). Note: If the boiler’s plug connected to this receptacle does not have 5 wires, then this second
zone feature is not available. See page 11 for instructions on selecting one of the following three operating
modes.
• Domestic Hot Water (DHW): During a call from an indirect water heater, the control will allow the boiler
to fire to the high limit setting. It will prioritize the DHW call by de-energizing the heating circulator in the
event there is also a call for heat. The control will re-energize the heating circulator when the indirect
tank is satisfied or if the boiler temperature reaches 170°F. If the indirect call continues for 45 minutes,
the control will override the priority function and re-energize the heating circulator to provide space
heating.
• Zone Heating: During a call from a second zone thermostat, the control will operate the second zone
as it does the primary zone; the Economy function (when Active) will regulate the boiler temperature
and no priority will be given to either zone.
• Primary/Secondary Circulator Operation: This mode of operation should only be used for boilers or
installations utilizing a primary/secondary piping system. When the control is set in this mode, the pri-
mary circulator will be controlled by pin 5 of the LINE VOLTAGE connector (See page 3) and the sec-
ondary circulator will be controlled by pin 4. The primary pump will turn on any time there is a call for
heat, DHW, or low limit. It will remain on after the call is gone until the boiler temp drops to 120°F. The
secondary pump will turn on when there is a call for heat (T-T input) and the boiler temp is over 140°F. If
the secondary is on and the boiler temp drops below 130°F, the secondary pump will turn off. The sec-
ondary pump will not run on a call for DHW or if the control is off on warm weather shutdown. Note:
When the control is set for Primary/Secondary pump operation, program mode options 1 (Thermal Pre-
Purge) and 5 (Circulator hold off) will default to OFF.
2-ZONE CIRCULATOR OPTIONS