Heating Operation
Heat Demand signal
Selector switch = External Heat Demand
(a) - A heat demand signal is caused by either 24Vac applied to terminals Heat Dem — Heat Dem
(1 and 2), or a 10K Zone Control connected to terminals 10K Sen — Com Sen (19 and 20),or both.
(b) - A heat demand signal is either continuously present or, when a 10K Zone Control is connected,
then a heat demand signal is only present when the Zone Control calls for heat.
tekmar Zone Control function
Selector switch = Zone Control
The control will monitor the indoor temperatures of all zones, as well as the outdoor and supply
temperatures, and shift the Heating Curve (and the WWSD point) up or down to fine adjust the system
supply water temperature for whichever zone requires the hottest supply water. The Occupied and
Unoccupied dials are not functional.
Occupied/Unoccupied dial function (no indoor temperature feedback)
The control will monitor the outdoor and supply temperatures. The Occupied or Unoccupied dial settings become the WWSD point.
When the outdoor temperature is warmer than the setting of the Occupied dial, the control enters WWSD. When switched into
Unoccupied mode, the "Unoccupied' light will come on, and the control will operate at the temperature of the Unoccupied dial setting.
With Heat demand signal
The "Heat Demand" light will come on, the control will switch on the system pump and calculate the desired supply temperature based
on the requirements of the Heating Curve or the Minimum Supply setting, whichever is highest.
3
Sequence of Operation
When the Two Stage Boiler & DHW Control 252 is powered-up, the "Power" light will come on and the control will cycle through an
automatic test routine described in detail on pages 10 and 11 of this brochure. When the test routine is completed and no errors are
detected, the control exits the test routine and enters the operating mode.
Once in operating mode, the control uses the Outdoor Sensor 070 to continually monitor the outdoor temperature and the Universal
Sensor 071 to continually monitor the system supply water temperature. An optional Universal Sensor 071 can be installed to allow the
control to monitor a DHW tank temperature.
Indoor temperature can be monitored through the use of;
(a) - a tekmar Zone Control (switch selector switch to "Zone Control" position), or;
(b) - an Indoor Sensor 074 or a tekmar 2k RTU (switch selector switch to "Indoor Sensor" position).
While monitoring all of these temperatures, the control recognizes the following temperature conditions and inputs and will respond as
described. During operation, the lights of the control will indicate operational status as illustrated.
WWSD function
When WWSD occurs, the "WWSD" light will come on, and the control will continue to
monitor the outdoor temperature, supply temperature and indoor temperature (optional).
Whenever 3 days pass with the control in uninterrupted WWSD, the system pump will be
cycled on for 20 seconds to help prevent it from seizing up.
Outdoor temperature cold enough to require heating
No heat demand signal
When the outdoor temperature is colder than the WWSD point, the control will leave WWSD.
Whenever the control leaves WWSD, the "WWSD" light will turn off and the control will
continue to monitor the outdoor temperature, supply temperature and indoor temperature
(optional), but no further control action will take place until there is a heat demand signal.
Power
Heat
Demand
DHW
Demand
WWSD
Stage 1
Stage 2
UnOcc.
Minimum
DHW
pump
System
pump
Power
Heat
Demand
DHW
Demand
WWSD
Stage 1
Stage 2
UnOcc.
Minimum
DHW
pump
System
pump
Power
Heat
Demand
DHW
Demand
WWSD
Stage 1
Stage 2
UnOcc.
Minimum
DHW
pump
System
pump
Power
Heat
Demand
DHW
Demand
WWSD
Stage 1
Stage 2
UnOcc.
Minimum
DHW
pump
System
pump
1
2
3
4
5
6
7
8
Auto
Stage
1 2
Perm. Heat Demand
External Heat Demand
Indoor sensor
Zone control
DHW during unoccupied
DHW priority
Rotate
Off
DHW valve
DHW pump
1
2
3
4
5
6
7
8
Auto
Stage
1 2
Perm. Heat Demand
External Heat Demand
Indoor sensor
Zone control
DHW during unoccupied
DHW priority
Rotate
Off
DHW valve
DHW pump
1
2
3
4
5
6
7
8
Auto
Stage
1 2
Perm. Heat Demand
External Heat Demand
Indoor sensor
Zone control
DHW during unoccupied
DHW priority
Rotate
Off
DHW valve
DHW pump
1
2
3
4
5
6
7
8
Auto
Stage
1 2
Perm. Heat Demand
External Heat Demand
Indoor sensor
Zone control
DHW during unoccupied
DHW priority
Rotate
Off
DHW valve
DHW pump
Indoor Sensor 074 function
Selector switch = Indoor Sensor
The control will monitor the indoor, outdoor and supply temperatures, shifting the Heating Curve (and
the WWSD point) up or down to fine adjust the system supply water temperature whenever the room
temperature is different than the setting of the Occupied dial. In the Unoccupied mode, the "Unoccupied"
light will come on, and the control will maintain the room at the temperature of the Unoccupied dial setting.
Unoccupied mode
Connect (short circuit) terminals
Com Sen — UnO Sw (17 and 18) together.
The Occupied dial becomes inactive. The Unoccupied dial becomes active
2K RTU function
Selector switch = Indoor Sensor
The control will monitor the indoor, outdoor and supply temperatures, and shift the Heating Curve (and
the WWSD point) up or down to fine adjust the system supply water temperature whenever the room
temperature is different than the setting of the RTU dial. The Occupied and Unoccupied dials are not
functional, and a setback RTU must be used if Unoccupied schedules are desired.
1
2
3
4
5
6
7
8
Auto
Stage
1 2
Perm. Heat Demand
External Heat Demand
Indoor sensor
Zone control
DHW during unoccupied
DHW priority
Rotate
Off
DHW valve
DHW pump
16
DHW
Sen
Out
Sen
22
21
Sup
Sen
20
Com
Sen
19
10K
Sen
15
2K
RTU
17
Com
Sen
18
UnO
Sw
Selector switch = Perm. Heat Demand
OR