Tekmar Boiler Control 275 User manual

1 of 48 © 2012 D275 - 01/12
Boiler Control 275
D275
01/12
Replaces:03/09
Installation & Operation Manual
Multi-Staging
The Boiler Control 275 is designed to stage up to four condensing or non-condensing, modulating or on-off boilers using
P.I.D. staging to accurately maintain temperature. The control supports hybrid boiler plants that contain both condensing
and non-condensing boiler groups. Water temperature is controlled by outdoor reset for space heating applications or a
fixed setpoint for Domestic Hot Water (DHW) tank heating or industrial process heating applications. The control will also
accept an analog signal from an Energy Management System (EMS) to control the water temperature. Boiler equal run-time
rotation, pump exercising and stand-by system pump operation increase boiler plant reliability. The control is tekmarNet®
communication compatible allowing for internet connectivity using an optional Gateway 483.
tN4 Compatible
BTC I Compatible
24 Hour, 5-11, 5-2, 7 Day Schedule
Flow or Combustion Air Proof
Four Modulating or On/Off Boilers
•
•
•
•
•
Equal Run Time Rotation
Primary Pump Sequencing
DHW Operation
Optional DHW Sensor
Setpoint Operation
•
•
•
•
•
Additional functions include:
Setback
Boiler Control 275
One tN4, Four Modulating Boiler & DHW / Setpoint
Menu Item
Test
Boiler Demand
DHW / Setpoint Demand
Proof Demand
EMS Input Signal
Priority Override
Power 115 V ±10% 60 Hz 7 VA, 1150 VA max.
Relays 230 V (ac) 5 A 1/3 hp
Demands 20 to 260 V (ac) 2 VA
Designed and assembled in Canada by
tekmar Control Systems Ltd
tektra 1020-01
Meets Class B:
Canadian ICES
FCC Part 15
For maximum heat,
press and hold Test
button for 3 seconds.
not testing
testing
testing paused
off
red
red
BTC I
Off
EMS Rotate Fixed Last
Pump Sequencer
Exercise
Off
Demands
Date Code
H2048B
Signal wiring must be rated at least 300 V.
DHW
29
/SetpCom
30
Dem Pr.
31
Dem
2
–
5
–
Mod1
1
+Mod2
3
+
–+Mod3
4
+Mod4
6
+
BRet/
7
Com
8
tN4
12
Boil
9
Out
10
Com
11
Prim
P1 L N
26
Power
28271413
Do not apply power
24
DHW
/ P2
23 251615 1817 2019 2221
Fixed Lead
First On / Last Off
First On / First Off
Relay
1Relay 2Relay 3Relay 4C.A. / Alert Boiler Demand
Sup DHW
Zone Load Shedding
Input
Universal
Sensor
Included
Input
Universal
Sensor
Included
tN4
Boiler
Bus
Input
Outdoor Sensor
Included
OR
0-10 or 2-10 V (dc)
from EMS
Output
Up to 4
Modulating
Boilers
Input
115 V (ac)
Power Supply
Input
Flow OR
C.A. Proof
Output
Up to 4
Boiler Pumps
OR Boiler Enable
Output
DHW Pump
OR
Primary Pump
Output
Combustion
Air Damper
OR Alert
OR
OR
Output
Primary
Pump
Input
DHW OR
Setpoint
Demand
Signal
Input
Boiler
Demand
Signal

© 2012 D275 - 01/12 2 of 48
How to Use the Data Brochure
Table of Contents
This brochure is organized into three main sections.
They are: 1) Sequence of Operation,
2) Installation,
3) Control Settings and
4) Testing and Troubleshooting.
The Control Settings section of this brochure describes
the various items that are adjusted and displayed by the
control. The control functions of each adjustable item are
described in the Sequence of Operation.
User Interface...............................................................2
Display and Symbol Description...................................3
Access Level.................................................................4
Sequence of Operation.................................................4
Section A: Boiler Demand........................................4
Section B: Outdoor Reset......................................... 4
Section C: Boiler Operation......................................6
Section D: Modulating Boilers..................................8
Section E: On / Off Boilers ..................................... 10
Section F: OEM Boilers Equipped With A BTC I.... 10
Section G: Fixed Lead and Fixed Last ................... 10
Section H: Condensing and Non-Condensing Boiler
Groups ................................................................... 10
Section I: Domestic Hot Water Operation .............. 11
Section J: Setpoint Operation ................................ 14
Section K: Energy Management System (EMS) .... 16
Section L: Pump Operation.................................... 17
Section M: Combustion Air and Alert Settings ....... 18
Section N: Setting the Schedule ............................ 19
Section O: Time Clock ...........................................20
Section P: Boost.....................................................20
Section Q: Exercising.............................................20
Section R: tekmarNet®4 Communication................20
Section S: Scene Operation................................... 21
Installation ..................................................................22
Control Settings .........................................................28
Cleaning the Control ..............................................28
DIP Switch Settings................................................28
VIEW Menu............................................................30
ADJUST Menu .......................................................32
TIME Menu.............................................................39
SCHEDULE Menu..................................................40
MISC Menu ............................................................43
Testing the Control......................................................44
Error Messages .......................................................... 45
Technical Data............................................................48
Limited Warranty ....................................................... 48
The control uses a Liquid Crystal Display (LCD) as the
method of supplying information. You use the LCD in
order to setup and monitor the operation of your system.
The control has four push buttons (Menu, Item, ▲, ▼) for
selecting and adjusting settings. As you program your
control, record your settings in the ADJUST menu table,
which is found in the second half of this brochure.
Menu
All of the items displayed by the control are organized
into five menus (View, Adjust, Time, Schedule, and Misc).
These menus are listed on the top left hand side of the
display (Menu Field). To select a menu, use the Menu
button. By pressing and releasing the Menu button, the
display sequences between the five menus. Once a menu
is selected, there will be a group of items that can be viewed
within the menu.
Item
The abbreviated name of the selected item will be displayed
in the item field of the display. To view the next available
item, press and release the Item button. Once you have
reached the last available item in a menu, pressing and
releasing the Item button will return the display to the first
item in the selected menu.
The items can be quickly scrolled through by holding the
Item button and then pressing the ▼ button. To rapidly
scroll through the items in the reverse order, hold the
Item button and press the ▲ button.
Adjust
To make an adjustment to a setting in the control, begin by
selecting the ADJUST, TIME, SCHEDULE or MISC menu
using the Menu button. Then select the desired item using
the Item button. Finally, use the ▲, and / or ▼ button to make
the adjustment.
Additional information can be gained by observing the
Status field of the LCD. The status field will indicate
which of the control’s outputs are currently active. Most
symbols in the status field are only visible when the
VIEW menu is selected.
User Interface

3 of 48 © 2012 D275 - 01/12
Display
PRIMARY PUMP
Displays when primary pump 1 or
primary pump 2 is in operation
BOILER
Displays which modulating output is
operating
LOCK
Displays when adjusting Access level if
Switch is set to lock.
WARNING
Displays when an error exists.
COMMUNICATION BUS
Displays when tN4 thermostats are
connected.
DHW PUMP
Displays when the DHW Pump is
operating
°F, °C, MINUTES, AM, %, PM,
HOURS
Units of measurement.
BOILER PUMP
Displays when the boiler pump 1, 2, 3,
or 4 are operating
COMBUSTION AIR DAMPER
Displays when the combustion air
damper relay is closed
SCHEDULE MASTER
Displays when the 275 is a schedule
master
WARM WEATHER SHUT DOWN
Displays when the control is in warm
weather shut down
MINIMUM & MAXIMUM
Displays when the boil target or the boil
supply is at a minimum or maximum
Schd Wake
UnOcc Sleep
Away
Schd, Wake, UnOcc, Sleep, Away
Displays the current event of a
schedule or scene
POINTER
Displays the control operation as
indicated by the text
Symbol Description
Item Field
Displays the current
item selected
Buttons
Selects Menus, Items
and adjusts settings
Number Field
Displays the current value
of the selected item
Status Field
Displays the current
status of the control’s
inputs, outputs and
operation
Menu Field
Displays the
current menu
Menu Item

© 2012 D275 - 01/12 4 of 48
Once the control receives a boiler demand it calculates a
target water temperature based on the characterized heating
curve to provide outdoor reset for space heating. The control
can receive a boiler demand three different ways:
1. By applying 20-260 V (ac) to the boiler demand
terminals (27 & 28) when the DIP switch is set to
Demands.
2. From an Energy Management System (EMS) by
applying a 0-10 or 2-10 V (dc) signal to terminals 2 &
3 when the DIP switch is set to EMS.
3. From a tN4 device. This requires a tN4 thermostat to
be wired to terminals 1 & 2 so that the call for heat
can go over the communication bus.
2827
Boiler
Demand
20-260 V (ac)
Demand
OR OR
0-10 or
2-10 V (dc)
from EMS tN4
Demand
23
–+
OutCom
21
–
tN4 Com
Boiler Demand Section A
Outdoor Reset Section B
Sequence of Operation
In a heating system, the rate of heat supplied to the building
must equal the rate at which heat is lost. If the two rates are
not equal, the building will either cool off or over heat.
The rate of building heat loss depends mostly on the outdoor
temperature. Outdoor Reset allows a hot water heating
system to increase the water temperature, adding heat to
the building, as the outdoor temperature drops. The rate
at which the water temperature is changed as a function
of outdoor temperature is defined by the characterized
heating curve.
Characterized Heating Curve
A characterized heating curve determines the amount the
target water temperature is raised for every 1°drop in outdoor
air temperature.
The characterized heating curve takes into account the
type of terminal unit that the system is using. Since different
types of heating terminal units transfer heat to a space using
different proportions of radiation, convection and conduction,
the supply water temperature must be controlled differently.
The control uses the terminal unit setting to vary the supply
water temperature to suit the terminal unit being used. This
improves the control of the air temperature in the building.
Boiler Characterized Heating Curve
Terminal
Unit
Boiler
Design
Boiler
Indoor
Outdoor
Design
Decreasing Outdoor Temperatures
Increasing Water Temperatures
The access level restricts the number of Menus, Items,
and Adjustments that can be accessed by the user. The
Access Level setting is found in the Miscellaneous (MISC)
Menu. Select the appropriate access level for the people
who work with the control on a regular basis. There are
three Access Level Settings:
User (USER): Select this access level for building
supervisors and other non-technical staff to prevent
unauthorized access to installer and advanced level
settings.
•
Installer (INST): Select this access level to limit some of
the settings available to the installer. This is the factory
default access level.
Advanced (ADV): Select this access level to have complete
access to all of the control settings. In the display menu
tables, the appropriate access level needed to view each
item is shown in the Access column.
Note: the Lock / Unlock switch on the front of the control
must be set to unlock to change the access level.
•
•
Access Level
In order for the control to have a target water temperature there must be a demand. There are three different demands the
control can have: boiler demand, DHW demand, and setpoint demand.

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Terminal Unit Setting in Adjust Menu
Select the appropriate terminal unit in the adjust menu.
This will change the shape of the characterized heating
curve to better match the heat transfer properties of that
specific terminal unit.
Hydronic Radiant Floor (HRF1)
A heavy or high mass, hydronic radiant floor system. This
type of a hydronic radiant floor is embedded in either a thick
concrete or gypsum pour. This heating system has a large
thermal mass and is slow acting.
Hydronic Radiant Floor (HRF2)
A light or low mass, hydronic radiant floor system. Most
commonly, this type of radiant heating system is attached to
the bottom of a wood sub floor, suspended in the joist space,
or sandwiched between the subfloor and the surface. This
type of radiant system has a relatively low thermal mass
and responds faster than a high mass system.
Fancoil (COIL)
A fancoil terminal unit or air handling unit (AHU) consisting
of a hydronic heating coil and either a fan or blower. Air is
forced across the coil at a constant velocity by the fan or
blower and is then delivered into the building space.
Fin–tube Convector (CONV)
A convector terminal unit is made up of a heating element
with fins on it. This type of terminal unit relies on the natural
convection of air across the heating element to deliver
heated air into the space. The amount of natural convection
is dependant on the supply water temperature to the heating
element and the room air temperature.
Radiator (RAD)
A radiator terminal unit has a large heated surface that is
exposed to the room. A radiator provides heat to the room
through radiant heat transfer and natural convection.
Baseboard (BASE)
A baseboard terminal unit is similar to a radiator, but has
a low profile and is installed at the base of the wall. The
proportion of heat transferred by radiation from a baseboard
is greater than that from a fin-tube convector.
Boiler Terminal Unit Defaults
When a terminal unit is selected for boiler zones, the
control loads default values for the boiler design, boiler
maximum supply, and boiler minimum supply temperatures.
The factory defaults can be changed to better match the
installed system. Locate the Terminal Unit setting in the
Adjust menu.
Terminal Unit BOIL DSGN BOIL MAX BOIL MIN
High Mass Radiant 120°F (49°C) 140°F (60°C) OFF
Low Mass Radiant 140°F (60°C) 160°F (71°C) OFF
Fancoil 190°F (88°C) 210°F (99°C) 140°F (60°C)
Fin-Tube Convector 180°F (82°C) 200°F (93°C) 140°F (60°C)
Radiator 160°F (71°C) 180°F (82°C) 140°F (60°C)
Baseboard 150°F (76°C) 170°F (77°C) 140°F (60°C)
Room Setting in Adjust Menu
The Room setting is the desired room air temperature,
according to the outdoor reset heating curve. The Room
setting parallel shifts the heating curve up or down to
change the target water temperature. Adjust the Room
setting to increase or decrease the amount of heat available
to the building. Once the heating curve has been set up
properly, the Room setting is the only setting that needs to
be adjusted. The default Room setting is 70°F (21°C), and
it can be adjusted for both the occupied and unoccupied
periods.

© 2012 D275 - 01/12 6 of 48
Outdoor Design Setting in Adjust Menu
The outdoor design temperature is typically the coldest
outdoor air temperature of the year. This temperature is
used when doing the heat loss calculations for the building
and is used to size the heating system equipment. If a cold
outdoor design temperature is selected, the supply water
temperature rises gradually as the outdoor temperature
drops. If a warm outdoor design temperature is selected,
the supply water temperature rises rapidly as the outdoor
temperature drops.
Boiler Indoor Setting in Adjust Menu
The boiler indoor design temperature is the indoor
temperature the heating designer chose while calculating the
heat loss for the boiler water heated zones. This temperature
is typically 70°F (21.0°C). This setting establishes the
beginning of the boiler characterized heating curve.
Boiler Design Setting in Adjust Menu
The boiler design supply temperature is the boiler water
temperature required to heat the zones at the outdoor design
temperature, or on the typical coldest day of the year.
(Default automatically changes based on terminal unit
setting)
Warm Weather Shut Down (WWSD) Setting in Adjust
Menu
Warm Weather Shut Down disables the heating system when
the outdoor air temperature rises above this programmable
setting. When the control enters into WWSD, the LCD will
indicate this in the status field. WWSD is only available
when the DIP switch = Demands. The boilers will operate
when a Domestic Hot Water (DHW) demand or a Setpoint
Demand is present.
Boiler Operation Section C
The 275 is able to operate up to four modulating or on-off
boilers as a heat source. For proper operation of the boilers,
the 275 must be the only control that determines when a
boiler is to fire.
*Important note: The boiler operator, or aquastat, remains
in the burner circuit and acts as a secondary upper limit
on the boiler temperature. The boiler aquastat temperature
setting must be adjusted above the 275’s boiler maximum
setting in order to prevent short cycling of the burner.
Boiler Target Temperature
The boiler target temperature is determined by connected tN4
devices or by a Boiler, DHW or Setpoint demand received
by the control. An Energy Management System (EMS) can
also give a boiler target. The tN4 devices determine the
highest water temperature required and then request this
temperature on the tN4 boiler bus. The temperature request
creates a Boiler Demand and this is indicated on the display.
A DHW demand and a Setpoint demand have temperature
settings to which the boilers are operated to meet and are
able to override the tN4 bus temperature if required. The
control displays the temperature that it is currently trying to
maintain as the boiler supply temperature in the View menu.
If the control does not presently have a requirement for heat,
it does not show a boiler target temperature. Instead, “– – –”
is displayed in the LCD.
Boiler Minimum Setting in Adjust Menu
The boiler minimum is the lowest temperature that the
control is allowed to use as a boiler target temperature.
During mild conditions, if the control calculates a boiler
target temperature that is below the boiler minimum setting,
the boiler target temperature is adjusted to at least the
boiler minimum setting. The MIN segment is displayed in
the LCD while viewing the boiler supply or target and when
the boiler target is boiler minimum and the boiler supply is
less than boiler minimum plus 5°F (2.5°C). Set the Boiler
Minimum setting to the boiler manufacturer’s recommended
temperature.
Boil MIN
MIN segment on
Boil MIN + 5°F (2.5°C)
Boiler Differential
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Boiler Maximum Setting in Adjust Menu
The boiler maximum is the highest temperature that the
control is allowed to use as a boiler target temperature.
The MAX segment is displayed in the LCD while viewing
the boiler supply or target and when the boiler target is
boiler maximum and the boiler supply is greater than boiler
maximum minus 5°F (2.5°C). Set the boiler maximum
setting below the boiler operator or aquastat temperature.
At no time does the control operate the boiler above 248°F
(120°C).
Boil MAX
Boil MAX – 5°F (2.5°C)
Boiler Differential
MAX
segment
on
MAX
segment
on
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7 of 48 © 2012 D275 - 01/12
Stage Delay Setting in Adjust Menu
The Stage Delay is the minimum time delay between the
firing of each stage. After this delay has expired the control
can fire the next stage if it is required. This setting can be
adjusted manually or set to an automatic setting. When the
automatic setting is used, the control determines the best
stage delay based on the operation of the system.
Boiler Relay Setting in Adjust Menu (per boiler)
The 275 provides a dry contact for either burner ignition or
boiler pump. Selection is made through the Boiler RELAY
setting in the adjust menu. Select ‘burner’ for boilers that
require a boiler enable signal as well as a modulating signal
in order to operate. Select pump to operate a boiler pump
with post purge capabilities.
Boiler Mass Setting in Adjust Menu (per boiler)
Match the boiler mass setting with the thermal mass
characteristics of each boiler. The modulation of the boiler
can become unstable if the incorrect Boiler Mass setting is
chosen. A key sign of unstable boiler modulation is that the
flame will continue to increase and then decrease in short
periods of time. By choosing a lower boiler mass setting,
the boiler response will become more stable.
LO
The LO setting is selected if the boiler that is used has
a low thermal mass. This means that the boiler has very
small water content and has very little metal in the heat
exchanger. A boiler that has a low thermal mass comes
up to temperature quite rapidly when fired. This is typical
of many copper fin-tube boilers.
The Lo mass setting provides a fast response to the heating
system.
MED
The MED setting is selected if the boiler that is used has
a medium thermal mass. This means that the boiler either
has a large water content and a low metal content or a
low water content and a high metal content. This is typical
of many modern residential cast iron boilers or steel tube
boilers.
The Med mass setting provides a moderate response to
the heating system.
HI
The HI setting is selected if the boiler that is used has a
high thermal mass. This means that the boiler has both
large water content and a large metal content. A boiler that
has a high thermal mass is relatively slow in coming up to
temperature. This is typical of many commercial cast iron
and steel tube boilers.
The Hi mass setting provides a slow response to the
heating system.
Boiler Differential Setting in Adjust Menu
A modulating boiler must be operated with a differential
while operating at Minimum Modulation. When the boiler
is modulating above Minimum Modulation, the differential
does not apply. Instead, the modulation output signal is
determined using Proportional, Integral, and Derivative (PID)
logic in order to satisfy the boiler target temperature.
The boiler differential can be fixed or automatically
determined by the control. The Auto Differential setting
balances the amount of temperature swing in the boiler
supply temperature with boiler on times, off times, and
cycle times. This reduces potential short cycling during
light load conditions.
Manual Differential
Differential = 10°F (6°C) Target + 1/2 Differential
Target – 1/2 Differential
Target
165°F (74°C)
160°F (71°C)
155°F (68°C)
Boiler
On Boiler On
Automatic Differential
Off
Differential
Time
Heating Load
On
Rotation
The Rotate feature changes the firing order of the boilers
whenever one boiler accumulates 48 hours more run time
than any other boiler. Rotation will be forced if any boiler
accumulates 60 hours more run time. After each rotation,
the boiler with the least running hours is the first to fire and
the boiler with the most running hours is the last to fire.
This function ensures that all of the boilers receive equal
amounts of use. When the Rotate / Off DIP switch is set
to the Off position, the firing sequence always begins with
lowest boiler to the highest boiler.
720 hours
1 2
672 hours 720 hours
2 1
672 hours
To reset the rotation sequence (without regard to historical
running hours), toggle the Rotation DIP Switch Off for 3
seconds and on again. Note that the running hours (see
Run Time) in the View menu also need to be reset if you
want the rotation sequence and running hours display to
be synchronized.
Boiler Run Time in View Menu
The running time of each boiler is logged in the view menu.
To reset the running time, select the appropriate Boiler Run
Time in the View menu and press and hold the Up and
Down buttons together until CLR is displayed.

© 2012 D275 - 01/12 8 of 48
Modulating Boilers Section D
The 275 can operate up to four modulating boilers. The
control also provides dry contacts for either burner ignition
or boiler pump. Selection is made through Boiler Relay
setting in the Adjust menu.
Once a boiler is required to operate, the control outputs
an analog signal corresponding to the Start Modulation
setting and then turns on the boiler relay. Once the Fire
Delay time has elapsed, the modulating output is adjusted
to the Minimum Modulation setting. The control then holds
the modulating output at Minimum Modulation until the
Minimum Modulation Delay time has elapsed. Proportional,
Integral and Derivative (PID) logic is used in order to satisfy
the boiler target temperature.
Modulation Mode Setting in Adjust Menu
The control includes a Modulation Mode setting that
selects either Sequential or Parallel Modulation. Sequential
modulation should be used on boilers that are more efficient
when operating at high fire. Parallel modulation should be
used on boilers that are more efficient when operating at
low fire.
Sequential Modulation
In sequential modulation, the first boiler is turned on and
is modulated to satisfy light loads. Once the first boiler
does not have enough capacity to satisfy the load, the first
boiler reduces its modulation to provide a smooth transition
when the second boiler fires at low fire. The first boiler
then modulates up to maximum modulation as the load
increases. Only then is the second boiler able to increase
its output as the load continues to increase. When the third
boiler is required, the second boiler reduces its modulation
to allow the third boiler to operate at low fire. As the load
continues to increase, the second boiler is modulated to
its maximum and then the third boiler is modulated. The
operation is reversed when shutting off the boilers.
100% 60% Off Off
Parallel Modulation
In parallel modulation, the first boiler turns on at low fire
and begins to increase its modulation. Once the first boiler’s
output is greater than the combined output of the first and
second boiler’s low fire, the first boiler is modulated down
to low fire and the second boiler is fired at low fire. The
two boilers now modulate together. Once the two boiler’s
combined output is greater than the combined output of
all three boilers operating at low fire, the first and second
boilers are modulated down to low fire, and all three boilers
are operated at low fire. The boilers are then modulated
as the load increases. The operation is reversed when
shutting off the boilers.
40% 40% 40% 40%
Boiler Start Modulation Setting in Adjust Menu
(per boiler)
The Start Modulation setting is the lowest modulation
output required to obtain proper ignition. Whenever boiler
operation is required, the control outputs an analog signal
corresponding to the Start Modulation setting and closes
the boiler contact to turn on the burner. After the Fire Delay
has elapsed and the burner is ignited, the control modulates
the firing rate between the Minimum Modulation setting and
the Maximum Modulation setting.
Boiler Fire Delay Setting in Adjust Menu
(per boiler)
The Boiler Fire Delay sets the time it takes for the boiler to
generate flame from the time the boiler turns on.
Boiler Contact Closed
Time
Fire Delay
Burner On
Boiler Motor Speed Setting in Adjust Menu
(per boiler)
The Motor Speed is the amount of time the boiler requires
to go from 0% modulation to 100% modulation.
Gas valve actuating motors have a design time from
fully closed to fully opened which can be found in the
manufacturer’s manual. The Motor Speed should be set
to this time.
The Motor Speed setting for a Variable Frequency Drive
(VFD) is the amount of time required to go from a stopped
position to 100% fan speed. Since a VFD has a very quick
response rate, it may be necessary to increase the Motor
Speed setting in order to increase the stability of the boiler
modulation.
OR
Boiler % Modulation in View Menu
View the current % modulation of each boiler in the View
menu.

9 of 48 © 2012 D275 - 01/12
Boiler Minimum Modulation Setting in Adjust Menu
(per boiler)
The Minimum Modulation setting is the lowest modulation
output to obtain low fire. The Minimum Modulation setting
is typically based on the turndown ratio of the boiler. The
control adjusts the modulating output signal from Minimum
Modulation to 0% after the burner turns off and boiler
operation is not required.
To calculate the Minimum Modulation, use the following
formula:
For 0 to 10 V (dc):
Minimum
Modulation =
0V(dc) – Boiler’s Minimum
Input Signal x100%
0 – 10 V (dc)
Example:
A boiler requires a 1.8 V (dc) signal to fire the boiler at
low fire. The boiler can be modulated to 10 V (dc) where it
reaches high fire. This means the boiler’s input signal range
is 1.8 to 10 V (dc). The 275 control has an output signal
range of 0 to 10 V (dc).
To make the two signal ranges the same, the Minimum
Modulation required is:
Minimum Modulation = (0 – 1.8) ÷ (0 – 10) x 100% = 18%
Control’s
Output
Signal
Range
Boiler’s
Input
Signal
Range
100%
10 V (dc) 10 V (dc)
0 V (dc)
88%
Boiler’s
Minimum
Input
Signal
Minimum
Modulation
0%
1.8 V (dc)
18%
Minimum Modulation Delay Setting in Adjust Menu
(per boiler)
The Minimum Modulation Delay is the time that the boiler
burner must hold the modulation of the boiler at a minimum
before allowing it to modulate any further.
Boiler Maximum Modulation Setting in Adjust Menu
(per boiler)
The Maximum Modulation defines the maximum output
signal from the control to the boiler burner. It is based on
a percentage of the control’s output signal range. The
maximum modulation setting for boilers with power burners
is typically set to 100%.
For boilers with electronic operators, the boiler’s input signal
range may not match the output signal range of the 275
control. The Maximum Modulation setting limits the control
output range in order to match the boiler’s input range.
To calculate the Maximum Modulation, use the following
formula:
For 0 to 10 V (dc):
Maximum
Modulation =
0V(dc) – Boiler’s Maximum
Input Signal x100%
0 – 10 V (dc)
Example:
A boiler’s input signal range is 0 to 9 V (dc). The 275
control has an output signal range of 0 to 10 V (dc). To
make the two signal ranges the same, the Maximum
Modulation required is:
Maximum Modulation = (0 – 9) ÷ (0 – 10) x 100% = 90%
Control’s
Output
Signal
Range
Boiler’s
Input
Signal
Range
100%
10 V (dc)
9 V (dc)
0 V (dc)0 V (dc)
88%
Boiler’s
Maximum
Input
Signal
Maximum
Modulation
0%
Minimum and Maximum Boiler Outputs (MBH)
Setting in Adjust Menu
(per boiler)
In order to accommodate different boiler capacities in the
same system, a minimum and maximum boiler output
for each boiler can be set. This allows the control to
properly operate the boilers using either sequential or
parallel modulation. Each boiler typically has a rating plate
that specifies the minimum and maximum output. This
information is also available in the boiler manual.
The minimum and maximum boiler output is expressed
in MBH. 1 MBH = 1,000 BTU / hour. The range is from 1
MBH to 1,999 MBH.
For example, if a boiler has a maximum output of 100,000
BTU / hr and a minimum output of 20,000 BTU / hr (turn
down ratio of 5):
Maximum Boiler Output = 100,000 = 100 MBH
1,000
Minimum Boiler Output = 20,000 = 20 MBH
1,000

© 2012 D275 - 01/12 10 of 48
On / Off Boilers Section E
OEM Boilers Equipped With A BTC I Control Section F
The 275 can sequence up to four boilers equipped with an
integral BTC I control. Boilers that include the BTC I control
may have multi-stage or modulating burners. Each boiler
is connected to the 275 using two wires connected to the
Mod + and - wiring terminals for each boiler stage. The 275
also allows combinations of multi-stage boilers together with
modulating boilers. In total, the 275 is able to control up to
16 stages. For information on BTC I equipped boilers and
how to installed with the 275, please see tekmar Service
Bulletin SB 055.
The 275 can operate up to four modulating or on/off boilers
in any combination. Each boiler stage has a Boiler Mode
setting in the the Adjust menu that allows the selection of
either modulating (Mod) or on/off (OnOF). By selecting a
boiler stage to on/off, the 275 then uses sequential boiler
staging, the stage relay is set to operate a burner, and
settings related to modulation are removed from the boiler
settings.
Fixed Lead and Fixed Last Section G
Condensing and Non-Condensing Boiler Groups Section H
Fixed Last
In some applications, it may be desirable to have the last
boiler fire last at all times while the firing sequence of
the remaining boilers is changed using Equal Run Time
Rotation. This configuration is typical of installations where
the boiler plant includes higher efficient boilers and a single
lesser efficient boiler. The lesser efficient boiler is only
desired to be operated when all other boilers in the plant are
on and the load cannot be satisfied. This rotation option is
selected by setting the Fixed Last / Off DIP switch to Fixed
Last. With a fixed last rotation, the last boiler is the last to
stage on and the first to stage off. The Fixed Last is always
applied to the boiler 4 output.
Fixed Lead & First On / First Off
In some applications, it may be desirable to have the first
boiler fire first at all times while the firing sequence of
the remaining boilers is changed using Equal Run Time
Rotation. This rotation option is selected by setting the Fixed
Lead / Off DIP switch to the Fixed Lead position. The Fixed
Lead is always applied to the boiler 1 output.
When using the Fixed Lead rotation option, a selection must
be made between First On / Last Off and First On / First
Off using the DIP switch.
When First On / First Off is selected, the lead boiler is always
staged on first and staged off first. This configuration is
typical of installations where the boiler plant includes similar
boilers but the first boiler is required to be the first to fire in
order to establish sufficient draft for venting.
Fixed Lead & First On / Last Off
When First On / Last Off is selected, the lead boiler is
always staged on first and staged off last. This configuration
is typical of installations where the boiler plant includes a
single higher efficient boiler with lesser efficient boilers.
The lead boiler is the high efficiency boiler, therefore it the
last boiler to be sequenced off.
Operating a boiler plant that contains both condensing
(high initial cost) and non-condensing (lower intial cost)
boilers allows the boiler plant to achieve nearly the same
operating efficiencies as operating all condensing boilers
but at a much lower installed cost to the building owner.
High system efficiency can be acheived as long as the
condensing boilers are the first to operate in the firing
sequence. During mild weather, the lead condensing boilers
operate at lower boiler temperatures and achieve their peak
boiler effiencies while the non-condensing boilers are rarely
operated. During very cold weather, the boiler target is often
above the boiler’s condensation point and the condensing
and non-condensing boilers operate together at roughly
the same efficiency level.
The 275 supports the operation of condensing and non-
condensing boilers as separate groups through either the
Fixed Lead or Fixed Last options. When a condensing
boiler is operating, it is desirable to operate the boilers
without a boiler minimum temperature being applied to the
boiler target. This allows the condensing boiler to operate
at its maximum efficiency. When a non-condensing boiler
is operating, a boiler minimum temperature should be
applied to the boiler target to prevent damage to the non-
condensing boiler heat exchanger from sustained flue gas
condensation.
To operate one to three condensing boilers as the lead
boiler group, and operate a single non-condensing boiler
as the lag boiler, set the Fixed Last / Off DIP switch to the
Fixed Last position and select the Condensing Lead (COND
LEAD) setting to on. The boilers within the condensing lead
group can be operated using Equal Run Time Rotation to
balance running hours.
To operate a single condensing boiler as the lead boiler,
and operate one to three non-condensing boilers as the lag
group, set the Fixed Lead / Off DIP switch to the Fixed Lead
position and select the Condensing Lead (COND LEAD)
setting to on. The boilers within the non-condensing lag
group can be operated using Equal Run Time Rotation to
balance running hours.
In the event that Fixed Lead or Fixed Last is selected and
all boiler are non-condensing, select the Condensing Lead
(COND LEAD) setting to off.