POWERING UP THE CONTROL
When the Boiler Control 256 is powered up, the control displays the
control type number in the LCD for 2 seconds. Next, the software version
is displayed for 2 seconds. Finally, the control enters into the normal
operating mode, and the LCD defaults to displaying the current outdoor
air temperature.
OPERATION
The 256 operates a single on / off heat source to control the supply
water temperature to a hydronic system. The supply water temperature
is based on the current outdoor air temperature and the
Characterized
Heating Curve
settings.
SETBACK (UNOCCUPIED)
To provide greater energy savings, the 256 has a setback capability. With setback, the
supply water temperature in the system is reduced when the building is unoccupied. By
reducing the supply water temperature, air temperature in the space may be reduced
even when thermostat(s) are not turned down. Any time the
Com
(3) and the
UnO Sw
(4)
terminals are shorted together, the control operates in the unoccupied (Night) mode. When
in the unoccupied (Night) mode, the UNOCC segment is displayed in the LCD. The 256
adjusts the supply water temperature based on the UNOCC settings made in the control.
FACTORY DEFAULTS
The control comes preset with several factory defaults. These defaults are based on the terminal unit selection (see section B2). To
fine-tune building requirements, these defaults may be changed. If a factory default value for a terminal unit is changed, the terminal
unit number will flash when selected in the ADJUST menu.
To reload the factory defaults listed in section B2, power down the control and wait for 10 seconds. Power up the control while simultaneously
holding the
Item
and buttons. The terminal unit number should now be displayed constantly in the LCD rather than flashing.
Section A
General Operation
Page 4
Section B
Boiler Reset
Page 5-8
4 of 20
© 2019 tekmar 256_D - 09/19
Outdoor Design
Increasing W
ater
Temperature
Design Supply
Decreasing Outdoor Temperature
Terminal Unit
Indoor Design
3
4
Timer switch
Com UnO
Sw
Sequence of Operation
Section A — General Operation
