Introduction 1
Brief Description of Control Operation
The HS2105 is a heating system controller integrating the
functions of space heating on outdoor reset using an outdoor
sensor, priority domestic hot water heating (DHW) of an
indirect fired water heater, periodic operation of a DHW
recirculation pump as well as offering programmable night
setback for customized operation. Optional modules provide
2-stage or dual burner control and outdoor reset control of a
motorized mixing valve for floor heating applications.
Note: Buderus Hydronic Systems, Inc. strongly
recommends the use of a thermostatic valve on the
outlet of the DHW storage tank to prevent scalding
when operating the HS2105 in manual override mode.
Two different control methods can be utilized with respect to
space heating. Parameters listed in bold are set on the control.
Refer to relevant sections in this manual for more details.
Case 1: All heating zones are controlled by on/off
thermostats.
The space heating operates along a heating curve;
figure 1 shows a typical curve. The slope is set by the
“REF TEMP” value; the heating curve can be shifted
up or down with the “OFFSET”.The boiler maintains
temperature within the dashed lines of the burner
differential. The control uses the difference between the
specified “DAY TEMP” and “NIGHT TEMP” values
to compute a lower heating curve for night mode operation.
On a call for DHW, the control can fire the burner up
to the “MAX TEMP 1” setting for maximum recovery.
The control temporarily interrupts pump operation with
the burner running when the boiler water temperature
drops below the “PUMPLOGIC” setting for condensation
protection.
3
Fig. 1: Typical heating curves for the HS2105 without a room sensor
MAX TEMP1
Heating Curve
(day mode)
Heating Curve
(night mode)
Burner
Differential
Pump Logic
Offset
200
180
160
140
120
100
80
60
Ref Temp
70 60 50 40 30 20 14 10 0 -10 -20 -30
OUTSIDETEMPERATURE (˚F)
2
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