• 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-
ture 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
Sensor terminals. The Outdoor Sensor measures the outdoor air
temperature.
Boiler 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 temper-
ature. Using a small screwdriver adjust the
reset ratio knob to appropriate Outdoor Design
Temperature. When set to OFF, the boiler tem-
perature 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.
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
Ω
(1 k =
1000
Ω
) 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-
Ω
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.
OFF
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-10
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