Caution
Improper installation and operation of this control could result in damage to equipment and possibly even personal injury. It
is your responsibility to ensure that this control is safely installed according to all applicable codes and standards.
Step One
Getting ready
Check the contents of this package. If any of the contents listed are missing or damaged, please refer to the Limited Warranty and
Product Return Procedure on the back of this brochure and contact your wholesaler or tekmar sales agent for assistance.
Type 252 includes:
• One Control 252 • One Outdoor Sensor 070 • One Universal Sensor 071
• One Data Brochure D 252 • One Data Brochure D 001 • One Application Brochure A 252
Other information available:
• Essay E 001 • Essay E 002
Read Application Brochure A 252 and select the correct Application for your job.
Note:
Carefully read the details of the Application, and the Sequence of Operation sections in all applicable brochures to ensure that you have
chosen the proper control, and you understand its functions within the operational requirements of your system.
DHW Operation
DHW mode using DHW Sensor 071
• A DHW Sensor 071 must be installed in terminals
DHW Sen — Com Sen (16 and 17).
• The DHW Sensor causes the control to monitor the DHW tank temperature. The control generates a DHW demand when 5
minutes has elapsed from the last DHW operation and the tank temperature is dropping quickly, or over a longer period of time
when the tank temperature becomes cooler than the DHW dial setting. This DHW demand causes the control to maintain the
supply water temperature at the DHW dial s 20
°
F(11
°
C), and over time will increase the supply temperature to the DHW
dial s 40
°
F(22
°
C).
4
Heating Operation (cont.) — Outdoor temperature cold enough to require heating
With boiler minimum setting higher than heating curve requirement
The "Minimum" light will come on and the control will switch on the boiler(s). The boiler(s) will
fire until the supply temperature reaches the minimum setting plus the differential setting. When
this point is reached, the "Minimum" light will stay on and the control will cycle the boiler(s) to
maintain the supply water above the Minimum setting.
Outdoor temperature cold enough for heating curve operation
The "Stage" light(s) will come on and the control will fire the boiler(s). The boiler(s) will fire until
the supply temperature reaches the heating curve desired temperature plus one half the dif-
ferential setting, where the "Stage" light(s) will turn off and the boiler(s) will be shut off.
Note: Whenever the boiler(s) are turned off, the control will keep them off until at least the
minimum time delay has expired
(1 minute to 5 minutes depending on degree of error).
DHW mode using external DHW Aquastat (no DHW Sensor)
• A 24Vac DHW Demand signal must be applied to terminals
DHW Dem — DHW Dem (3 and 4).
• The DHW Demand signal causes the control to maintain a supply water temperature at the DHW dial setting,
and over time can increase the supply temperature to the DHW dial s 20
°
F(11
°
C) .
DHW operation when control is not in heating mode
When there is a DHW demand, the "DHW Demand" light will come on and the control will operate the DHW
pump or System pump and DHW valve to generate DHW. The boiler(s) will be cycled to maintain the
temperature required by the DHW dial setting (above). When DHW demand is removed, the boiler(s) are
turned off but the pump continues to run for 1 minute to purge the remaining heat from the boiler(s).
DHW operation when control is in heating mode
When a DHW demand occurs, the "DHW Demand" light will come on and the control will operate the DHW
pump or System pump and DHW valve to generate DHW. The control will compare the heating curve desired
supply temperature against the DHW desired supply temperature and operate the boiler(s) to maintain the
supply at whichever is the hotter desired temperature.
DHW during unoccupied
selector switch #4 = On
When in Unoccupied mode, the control will operate (as above), to generate DHW.
No DHW during unoccupied
selector switch #4 = Off
DHW will not be generated in Unoccupied mode, even with a DHW Demand signal.
1
2
3
4
Dem Dem
Dem Dem
Heat
DHW
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
Installation
15
2K
RTU
19
20
10K
Sen
Com
Sen
21
22
Sup
Sen
Out
Sen
18
UnO
Sen
16
DHW
Sen
17
Com
Sen
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
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
