Install Instructions

Boiler Operation:
The supply water temperature from a boiler can be controlled by
cycling the boiler on and off. Modulation of the boiler’s operating
temperature in hot water heating systems not only provides more
comfort but also offers significant energy savings. The cooler the
boiler runs, the more efficient it is due to less heat losses up the flue
and reduced boiler jacket losses.
Differential:
An on / off boiler must be operated with a differential in order to pre-
vent short cycling. When the supply water temperature drops below
the bottom rail of the differential, the boiler is turned on. The boiler is
t
hen kept on until the supply water temperature rises above the top
rail of the differential. If the differential is too wide, there can be large
supply water temperature swings; however, if the differential is too
narrow, the boiler short cycles and operates inefficiently. This control
c
an be set for two different boiler differentials, 10°F (6°C) or 20°F
(12°C). This setting will help to achieve an appropriate balance
between temperature swings and boiler efficiency.
Minimum Boiler Supply:
Most boilers require a minimum supply water temperature in order to
prevent corrosion from flue gas condensation. The control should
therefore only modulate the boiler supply water temperature down to
the boiler manufacturer’s minimum recommended operating temper-
ature. Some boilers are designed to condense and should be oper-
ated at low water temperatures as much as possible for maximum
efficiency.
SUPPLY WATER TEMPERATURE
TIME
D
ifferential = 10
°F (5°C
)
165
°F(74°C)
155°F (68°C)
1
60°F (71°C)
B
OILER ON
B
OILER ON
BOILER OFF
B
OILER OFF
OUTDOOR AIR TEMPERATURE
50
(10)
30
(-1)
10
(-12)
-10
(-23)
70
(21)
90
(32)
W
WSD
TEMPERATURE
°
F(
°
C)
SUPPLY WATER TEMPERATURE
110 (43)
7
0 (21)
9
0 (32)
210 (99)
170 (77)
150 (65)
1
30 (54)
1
90 (88)
RESET
RATIO
B
OILER
M
INIMUM
SEQUENCE OF OPERATION:
Powering Up the Control:
After the SR501-OR is powered up, the green power LED light will be on.
Heating Demand:
The SR501-OR receives a heating demand from thermostat or zone
control end switch closure on the R and W thermostat terminals. The
thermostat red LED light will also be turned on. The control can be
setup for boiler temperature reset or ON – OFF boiler operation.
Reset Demand:
When the SR501-OR receives a heating demand the controls enable
the boiler based on the reset curve. The Boiler Relay red LED light
will be turned on when the boiler relay is energized.
DHW Demand:
When the SR501-OR receives a DHW demand the controls enable
the boiler and ignore the boiler reset curve. The DHW Override red
LED light will also be turned on.
Warm Weather Shut Down (WWSD):
When the outdoor temperature rises above 70°F (21°C), the control
turns off the boiler and blinks the Thermostat LED light. This function
only applies for space heating and does not affect DHW operation.
Boiler Operation:
When the SR501-OR has a reset demand, the system supply water
temperature is controlled by turning the boiler on and off. The control
calculates the target supply water temperature based on the outdoor
temperature, and the settings that were entered. The boiler operates
around a differential that is manually set by dip switch number 2. The
control includes a minimum on and off time for the boiler, in order to
minimize short cycling.
Maximum Boiler Supply:
The SR501-OR does not allow the boiler target temperature to
exceed the boiler design temperature setting plus 10°F (6°C) up to a
maximum of 225°F (107°C).
Minimum Boiler Supply:
The SR501-OR has a 140°F minimum boiler setting which is used in
order to prevent corrosion from flue gas condensation. During mild
outdoor conditions, the boiler cycles around the minimum boiler set-
ting. This programmed function can be set to the OFF setting for
condensing and electric boilers.
The sensor should be mounted on a wall which best represents
the heat load on the building (i.e. a northern wall for most build-
ings and a southern facing wall for buildings with large south
facing glass areas). The sensor should not be installed near heat
sources such as ventilation or window openings.
The sensor should be installed at an elevation above the ground
that will prevent accidental damage or tampering.
Install the Outdoor Sensor and run the wiring back to the con-
trol mounting location.
Installing the Boiler Sensor:
Note: This sensor is designed to mount on a pipe or in a tempera-
t
ure immersion well.
The sensor can be strapped directly to the pipe using the cable
tie provided. Insulation should be placed around the sensor to
reduce the effect of air currents on the sensor measurement.
The Boiler Sensor should be placed downstream of a pump or
after an elbow or similar fitting. This is especially important if
large diameter pipes are used because the thermal stratification
within the pipe can result in erroneous sensor readings. Proper
sensor location requires that the fluid is thoroughly mixed with-
in the pipe before it reaches the sensor.
Step Three:
Wiring to the Zone Control:
Line Voltage Connections –
Connect 120VAC incoming line voltage; Hot to the H terminal and
Neutral to the N terminal.
Connect 120VAC circulator; HOT lead of circulator to Zone H ter-
minal and Neutral lead of circulator to Zone N terminal.
Low Voltage Connections –
Connect thermostat or zone control end switch to the R and W
thermostat terminals.
Connect the DHW aquastat to the R and W DHW override terminals
(optional).
Connect boiler’s T and T terminal to the X and X boiler end switch
terminals.
Wiring the Sensors:
Do not apply power to these terminals as this will damage the
control.
Outdoor Sensor
Connect the two wires from the Outdoor Sensor to the Outdoor
S
ensor terminals. The Outdoor Sensor measures the outdoor air
temperature.
B
oiler Sensor
Connect the two wires from the Boiler Sensor to the Supply
Sensor terminals and insulate. The Boiler Sensor measures the
supply water temperature going from the boiler to the system.
SETTINGS:
Before adjusting the settings, read through the sequence of operation
to ensure that you understand how the control operates. The follow-
ing page describes how to program these settings into the control
once it has been powered up.
Step Four:
Outdoor Design Temperature:
The Outdoor Design setting is the outdoor temperature used in the heat
loss calculation. It is set to the typical coldest outdoor temperature.
Using a small screwdriver adjust the rest ratio knob to appropriate
Outdoor Design Temperature. When set to OFF, the boiler temperature
will not be reset and boiler will fire to high limit when there is a call for
heat.
Boiler Minimum Supply Temperature (Dip Switch #1):
Most boilers require a minimum operating temperature to prevent
corrosion from flue gas condensation. The minimum boiler dip switch
should be set to ON (140°F) supply water temperature so boiler can
operate without causing the boiler flue gases to condense. Consult
the boiler manufacturer for recommended minimum boiler supply
temperatures. The dip switch can also be set to OFF (70°F) when
condensation is not a concern.
Differential (Dip Switch #2):
The differential adjustment sets how far the actual boiler supply
water temperature may deviate from the desired temperature before
the boiler is turned on or off. This is a function of the water content
of the boiler and the flow rate through the system pump relative to
the heat output of the boiler. The differential can be set by dip switch
#2, set to OFF for 10°F (6°C) or set to ON for 20°F (12°C).
Pump Operation (Dip Switch #3):
The pump operation is controlled by dip switch #3. When the dip
switch is set to ON, the pump output will energize when thermostat
or DHW calls for heat. When set to OFF, the pump will only come on
when the thermostat calls for heat not the DHW.
Warm Weather Shut Down:
When the outdoor temperature rises above 70°F (21°C), the control
turns off the boiler and blinks the Thermostat LED light. This function
only applies for space heating and does not affect DHW operation.
INSTALLATION:
Step One:
Check the contents of this package. If any of the contents listed are
missing or damaged, please contact your sales representative for
assistance. The SR501-OR includes:
SR501-OR Boiler Reset Control and Switching Relay Combination
One Outdoor Sensor
One Strap on Sensor
Instruction Sheet
Replacement sensors are available from Taco, Inc.:
Strap on Sensor – 9300-2044RP
Outdoor Sensor 9300-2052RP
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:
Installing the Control:
The enclosure is to be mounted flush onto a wall or any ridge sur-
face.
The mounting holes in the enclosure accept #6 screws.
Line voltage to enter from bottom of control and low voltage to
enter from top of control.
Installing the Outdoor Sensor:
Note: The temperature sensor (thermistor) is built into the enclosure.
Use one round or pan head screw to attach the base of the sen-
sor to the wall.
The sensor is wall mounted and the wiring enters through the
bottom of the enclosure. The hole for the cable entry must face
downward in order to prevent water from entering and filling the
enclosure.
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 con-
trol 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 cer-
tified as safety limits must be part of the control circuit.
TROUBLESHOOTING:
Step Five:
As in any troubleshooting procedure, it is important to isolate a prob-
lem as much as possible before proceeding. The blinking error LED
light greatly simplifies troubleshooting of the SR501-OR. If you sus-
pect a wiring fault, return to step three and carefully check all exter-
nal wiring and wiring connections.
Sensor Errors:
If an outdoor sensor fault occurs, the SR501-OR will assume a
fixed outdoor temperature of 32°F (0°C) and will target the
appropriate supply water temperature. The Boiler light will blink
twice every 5 seconds to indicate the outdoor sensor error.
If a boiler sensor fault occurs, the SR501-OR turns the boiler off
and the Boiler light will blink once every 5 seconds to indicate
the boiler supply sensor error.
Adjustment of Settings:
If the outdoor temperature is cold and the rooms are cold,
increase the Outdoor Design setting by 5°F (3°C) per day.
If the boiler is cycling too often, increase the Differential setting.
Testing the Sensors:
A good quality test meter capable of measuring up to 5,000 k (1 k =
1000 ) is required to measure the sensor resistance. In addition to
this, the actual temperature must be measured with either a good
quality digital thermometer, or, if a thermometer is not available, a sec-
Do not apply voltage to a sensor at any time
as damage to the sensor may result.
Note: When the outdoor temperature rises above 70°F (21°C), the
control turns off the boiler and blinks the Thermostat LED light.
DHW will still operate.