© 2013
400_D - 09/13
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Setpoint Operation
Section D
A Setpoint Call is required in order for the control to provide
heat to a setpoint load, such as a spa, pool, or snowmelt
load. This can be done in two ways:
Contact Closure
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--------------------------------
A dry contact or 24 V (ac) signal is applied across the
Setpoint Call terminals on the 400.
tekmarNet
®
Setpoint Control with Sensor
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-------
A Setpoint Call is provided through the tekmarNet
®
system. This can be done through the tN4 Expansion
terminals with a setpoint device such as a Setpoint
Control 161.
Once the control registers a Setpoint Call, it will display
the “Setp” icon under Calls in the display.
Note:
Setpoint operation has a fixed priority of on.
Setpoint Operation
-----------------------------
-----------------------------
The control can operate to satisfy the requirements of a
setpoint load in addition to a space heating load and a
DHW load. A setpoint load overrides the current outdoor
reset temperature and WWSD setting in order to provide
heat to the setpoint load.
Setpoint Priority
Boiler System
Pump
Setpoint
Pump
Zone
Valve
Setpoint
ON
OFF
OFF
When the control receives a Setpoint Call:
All Boiler zones are turned off.
The boiler will operate to maintain the Setpoint tem-
perature as set in the Adjust menu, or as set on the
tekmarNet
®
Setpoint control if one is being used.
Setp
Calls
It is assumed that the Setpoint pump will provide adequate
flow through the heat exchanger and the boiler.
Setpoint calls will also be responded to when the system
is in
Away
, which can be set using a 479 User Switch.
Setpoint Priority Override
----------------------
----------------------
To prevent the building from cooling off too much or
the possibility of a potential freeze up during setpoint
priority, the control attempts to limit the amount of time
for setpoint priority.
As the outdoor air temperature becomes colder, the length
of time the control provides setpoint priority is reduced.
Once the allowed time for priority has elapsed, the control
will check the space heating target.
If there is a space heating target, the boiler operates at
that target for 15 minutes.
If after 15 minutes there is still a Setpoint Call, the con-
trol will, shut off all boiler heating zones and target the
Setpoint temperature.
Note: It is possible to disable Setpoint Priority by using
a tekmarNet
®
Setpoint control and turning the priority
to Off in the Setpoint control.
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Boiler Operation
Section E
The 400 is able to operate a single 1-stage or 2-stage on-
off boiler or a single modulating boiler as a heat source.
For proper operation of the boiler, the 400 must be the only
control that determines when the boiler is to fire.
*Important note:
The operating control in the boiler, also
known as an aquastat, remains in the burner circuit and acts
as a secondary upper limit on the boiler temperature. The
boiler operator temperature setting can be adjusted above
210°F, which is the fixed Boiler Maximum on the 400.
Boiler Target Temperature
----------------------
----------------------
The boiler target temperature is the temperature which
the control is trying to operate the boiler at. There are
four items that determine the boiler target temperature:
Boiler Call
DHW Call
Setpoint Call
If the control receives more than one call for heat at the
same time, it will operate the boiler at the highest of the
four calls.
•
•
•
The control displays the temperature that it is currently
trying to maintain as the boiler supply temperature in the
View menu. If the control does not presently have a call for
heat, it does not show a boiler target temperature. Instead,
‘– – –’ is displayed on the LCD.
Boiler Minimum
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--------------------------------
When operating non-condensing boilers, it is important
to prevent cool water from returning to the boiler. Cold
return temperatures create flue gas condensation, which
if left too long, can severely damage the boiler.
The 400 protects the boiler through the Boiler Minimum
setting. The boiler minimum is the lowest temperature that
the control is allowed to use as a boiler target temperature.
If the boiler is operating at the boiler minimum temperature,
the “MIN” segment is turned on in the display when viewing
either the boiler supply temperature or the boiler target
temperature.
