3
WARM WEATHER SHUT DOWN (WWSD)
When the outdoor temperature rises above the WWSD setting, the 253 flashes the
WWSD
pointer and turns off the
Boiler relay (4 and 5).
BOILER OPERATION
While the 253 has a heat demand, the system supply water temperature is controlled by turning the boiler on and off. The 253 calculates
the target supply water temperature based on the outdoor temperature, the heating curve setting, the starting temperature setting, the
WWSD setting, and the minimum boiler setting.
The boiler operates around a differential that is either manually set or automatically controlled by the 253. If the differential is manually
fixed and a heat demand is present, there is a 60 second off time delay of the boiler to allow for prepurging of the system and prevention
of boiler short cycling. The off time delay decreases to 20 seconds if the automatic differential is set. The automatic boiler differential
increases system efficiency by adjusting to changing loads.
Maximum Boiler Supply
The 253 does not allow the target boiler supply water temperature to exceed 220
°
F
(104
°
C) minus half the differential. If the boiler supply temperature reaches 220
°
F
(104
°
C), the control turns off the boiler.
Minimum Boiler Supply
The 253 has a
Minimum Boiler setting which selects a minimum target boiler supply
temperature in order to prevent corrosion from flue gas condensation. During mild outdoor
conditions, the boiler cycles around the minimum boiler setting. This programmed function
has an
Off setting for condensing and electric boilers. The control flashes the Minimum
Boiler pointer when operating at the minimum setting.
WWSD
Boiler Supply
Target Boiler
Starting Temp.
Minimum Boiler
Differential
Curve
F
OUTDOOR
H. Dem
Boiler
Installation
Caution
Improper installation and operation of this control could result in damage to the 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. This
electronic control is not intended for use as a primary limit control. Other controls that are intended and certified as safety
limits must be part of the control circuit.
STEP ONE
GETTING READY
Check the contents of this package. If any of the contents listed are missing or damaged, please contact your wholesaler or tekmar sales
representative for assistance.
Type 253 includes:
• One Stage Boiler Control 253
• One Outdoor Sensor 070
• One Universal Sensor 071
• Data Brochures D 253, D 001, D 070
• Application Brochures A 253
Other information available:
• Essays
Note Carefully read the details of the Sequence of Operation section in this brochure to ensure that you have chosen the proper control
for your application.
STEP TWO
MOUNTING
The control is mounted in accordance with the instructions in the Data Brochure D 001.
STEP THREE
ROUGH-IN WIRING
All electrical wiring terminates in the two wiring chambers on the control. If the control is to be mounted on an electrical box, the wiring
can be roughed-in at the electrical box prior to installation of the control. (See Brochure D 001.) Standard 18 AWG solid wire is
recommended for all low voltage wiring.
Power must not be applied to any of the wires during the rough-in wiring stage.
• Install the Outdoor Sensor 070 and the Universal Sensor 071 according to the instructions in the Data Brochure D 070 and run the
wiring back to the control mounting location.
• Run the wiring from the boiler to the control mounting location.
• Run the wires from the heat demand circuit to the control mounting location.
• Run the wires from the 24 V (ac) power source to the control mounting location.
Use a clean power source to ensure proper
operation.
Outdoor air temperature
50
(10)
30
(-1)
10
(-12)
-10
(-23)
70
(21)
3.6 3.0
2.0
1.6
1.2
0.8
0.4
0.6
90
(32)
°
F
(
°
C)
Supply water temperature
110
(43)
70
(21)
90
(32)
210
(99)
170
(77)
150
(65)
130
(54)
190
(88)
2.4
1.0
Starting
point
Minimum Boiler
Supply Setting
140
°
F
0.2
230
(110)
Maximum Boiler
Temperature 220
°
F
