Tekmar 420 User manual

D420
06/05
- Data Brochure
Boiler Reset Module 420
1 of 24 © 2005 D420 - 06/05
•
• tN4 Compatible
•
• Boiler Outdoor Reset
•
• Single On-Off or Modulating Boiler
•
• Powered Pump Outputs
•
• Setpoint Operation
•
• DHW Operation
•
• Includes Sensors
Features:
Information
Brochure
Choose controls
to match
application
1Application
Brochure
Design your
mechanical
applications
2Wiring
Brochure
Wiring and
installation of
specific control
4Job
Record
Record settings &
wiring details for
future reference
6
Data
Brochure
Control settings
and sequence of
operation
5
Rough-in
Wiring
Rough-in
wiring
instructions
3
The Boiler Reset Module 420 provides outdoor reset to a hydronic heating system in order to maximize comfort and
efficiency. The 420 can operate a single on / off boiler or a single modulating boiler. The 420 can override the outdoor reset
water temperature to provide Domestic Hot Water or Setpoint operations.
Introduction
51
52 53 54 55 56 57 58 60 61 62 63 64
Boiler DHW Setpoint C
59
C Com Boil OutVlv
Demand Demand 24 V (ac) DHW
R
65
+
Mod (dc)
–
DHW Primary
10 A
max.
66 67 68 69
N
Pump NPump
tN4
H7006B
Boil On-Off / Mod
Off / tekmar Stager
PoweredOutput 1 VA
DHW Valve:
24 V (ac) 8 VA
Made in Canada
Meets Class B: Canadian
ICES & FCC Part 15
Test
Boiler Reset Module 420
Item
Menu
tektra 991-01
Demands: 20 - 260 V (ac)
Relay Rating: 115 V (ac) 5 A
/
Do not apply power

© 2005 D420 - 06/05 2 of 24
Table of Contents
Table of Contents ...........................................................2
Display and DIP Switches ..............................................2
Dip Switch Settings ................................................2
Access Level...........................................................3
Display and Symbols Description ...........................4
User Interface ........................................................5
Display Menus................................................................6
View Menu ..............................................................6
Adjust Menu............................................................7
Miscellaneous Menu .............................................10
Testing the Control ....................................................... 11
Sequence of Operation................................................. 12
tekmarNet®4 Communication ............................... 12
Outdoor Reset ...................................................... 12
Boiler Temperature Control .................................. 14
tekmar Stager Operation ...................................... 17
Zone Load Shedding ............................................ 17
Domestic Hot Water Temperature Operation ....... 17
DHW with Low Temperature Boilers ..................... 19
Setpoint Temperature Operation...........................19
Pump Operation....................................................20
Error Messages ............................................................21
Troubleshooting ............................................................23
Warranty .......................................................................24
Set the DIP switch settings prior to making adjustments
to the control through the user interface. Setting the DIP
switches determines which menu items are displayed in
the user interface.
If you change a DIP switch setting while the control is
powered up, the LCD display returns to the View menu.
Lock/Unlock
Use the Lock/Unlock DIP switch to lock and unlock the Access
Level of the 420 and all connected tN4 devices, including
tN4 thermostats. For details, see “Access Levels”
•
• Once locked, the access level in all devices cannot be
viewed or changed.
•
• To determine if the control is currently locked a small
segment representing a padlock is viewed in the bottom
right hand corner of the display.
•
• To unlock the Access Level, set the DIP switch to
Unlock.
•
• To lock the Access Level, set the DIP switch to Lock.
Dip Switch Settings
Display and DIP Switches
51
52 53 54 55 56 57 58 60 61 62 63 64
Boiler DHW Setpoint C
59
C Com Boil OutVlv
Demand Demand 24 V (ac) DHW
R
65
+
Mod (dc)
–
DHW Primary
10 A
max.
66 67 68 69
N
Pump NPump
tN4
H7006B
Boil On-Off / Mod
Off / tekmar Stager
PoweredOutput 1 VA
DHW Valve:
24 V (ac) 8 VA
Made in Canada
Meets Class B: Canadian
ICES & FCC Part 15
Test
Boiler Reset Module 420
Item
Menu
tektra 991-01
Demands: 20 - 260 V (ac)
Relay Rating: 115 V (ac) 5 A
/
Do not apply power
6B
Boil On-Off / Mod
Off / tekmar Stager
/

3 of 24 © 2005 D420 - 06/05
Access Level
Boil On-Off/Mod
The Boil On-Off/Mod DIP switch selects whether the
control operates an On-Off boiler or the firing rate of a
Modulating boiler.
•
• If set to Boil On-Off, the control operates an On-Off
boiler.
•
• If set to Mod, the control operates a Modulating boiler.
tekmar Stager/Off
Use the tekmar Stager/Off DIP switch when a tekmar
staging control is be connected to the 420 in order to
operate multiple boilers. A tekmar stager may include
Boiler Controls 264, 265, and 268.
•
• If a tekmar Stager is installed, set to tekmar Stager.
When the tekmar Stager/Off DIP switch is set to tekmar
Stager, the Boiler Sensor DIP switch must be set to
Sup.
•
• If a tekmar Stager is not installed, set to Off.
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 two Access Level settings:
•
• Installer (InS): This is the factory default setting. This
access level is sufficient for the normal set up of the
control.
•
• Advanced (Ad): All of the control settings are available
to the user.
In the following menu tables, the access level the item is
visible in is shown in the access column.

© 2005 D420 - 06/05 4 of 24
PUMP
Displays when the primary or mixing pump
is in operation.
BURNER
Displays when the burner contact is
closed.
LOCK
Displays when the access levels are
locked.
WARNING
Displays when an error exists.
COMMUNICATION BUS
Displays when tN4 thermostats are
connected.
DHW PUMP
Displays when the DHW Pump is in
operation.
°F, °C, %, HOURS, MINUTES
Units of measurement.
BOILER DEMAND
Displays when a boiler demand is present.
DHW DEMAND
Displays when a DHW demand is present.
SETPOINT DEMAND
Displays when a Setpoint demand is
present.
DEVICE OUTPUT SCALE
Displays output of the modulating boiler.
Item Field
Displays an
abbreviated name
of the selected item
Number Field
Displays the
current value of
the selected item
Status Field
Displays the current
status of the control’s
inputs, outputs and
operation. Most symbols
in the status field are
only visible when the
VIEW Menu is selected
Menu Field
Displays the
current menu
Display
Symbols Description

5 of 24 © 2005 D420 - 06/05
User Interface
Continue
to next Item
Back to View Menu
Continue
to next Item
Continue
to next Item
Use the User Interface available on the Liquid Crystal Display
(LCD) to setup and monitor the operation of the system.
Use the four push buttons to the left of the LCD (Menu,
Item, Up, Down) to select settings. As you enter settings,
record the settings in the Job Record J420.
Menu
The menus display in the Menu Field at the top left side
of the LCD. Three menus are available: View, Adjust, and
Miscellaneous.
•
• To select a menu, press and release the Menu button.
Item
In each menu, a group of items can be selected. The
abbreviated name of the selected item displays in the Item
field of the LCD display.
•
• To view the next available item, press and release the
Item button.
•
• To view the previous item, hold down the Item button.
and press and release the Up button.
Adjusting a Setting
To adjust a setting:
1. Select the appropriate menu using the Menu button.
2. Select the item using the Item button.
3. Use the Up or Down button to make the adjustment.
Default Item
•
• To set the default item in the View menu, display the
item for more than five seconds.
After navigating menus, the display reverts back to the
default item after 60 seconds of button inactivity.

© 2005 D420 - 06/05 6 of 24
View Menu (1 of 1)
Item Field Range Access Description
-76 to 149°F
(-60.0 to 65.0°C)
InS
Ad
OUTDOOR SECTION B
Current outdoor air temperature as measured by
the outdoor sensor.
-22 to 266°F
(-30.0 to 130.0°C)
InS
Ad
BOILER SUPPLY SECTION C
Current boiler supply water temperature as measured
by the boiler sensor.
– – –, 35 to 230°F
(– – –, 1.5 to 110.0°C) Ad
BOILER TARGET SECTION C
The boiler target is the temperature the control is
currently trying to maintain at the boiler supply sensor.
“– – –” is displayed when no heat is required for boiler
zones.
0- 100% Ad
BOILER MODULATION SECTION C
Current percent modulation of the boiler’s burner.
Note: This item is only available when the Boiler
On-Off /Mod DIP switch is set to Mod.
0 to 9999 hr InS
Ad
BOILER RUN TIME
The total running time of the boiler since this item
was last cleared. To clear this item, press the Up
and Down buttons simultaneously while viewing
this item.
The View menu items display the current operating
temperatures and status information of the system.
VIEW MENU
Display Menus
After the last item, the control returns to the first item in the menu.

7 of 24 © 2005 D420 - 06/05
Item Field Range Access Description
-60 to 45°F
(-51.0 to 7.0°C)
Default = 10°F
(-12.0°C)
InS
Ad
OUTDOOR DESIGN SECTION B
The design outdoor air temperature used in the heat
loss calculations for the heating system. Typically set
to the temperature of the coldest day of the year.
1HRF1
2HRF2
3Fancoil
4Fin-tube Convector
5Radiator
6Baseboard
Default = 4
InS
Ad
BOILER TERMINAL SECTION B
The type of heating terminal units that are being
used in boiler zones.
40 to 100°F
(4.5 to 38.0°C)
Default = 70°F
(21.0°C)
Ad
BOILER INDOOR SECTION B
The design indoor air temperature used in the heat
loss calculation for the boiler zones. Typically set to
70°F (21.0°C).
70 to 220°F
(21.0 to 104.5°C)
Default = 180°F
(82.0°C)
InS
Ad
BOILER DESIGN SECTION B
The supply water temperature required for boiler
zones on the typical coldest day of the year.
OFF, 80 to 180°F
(OFF, 26.5 to 82.0°C)
Default = 140°F
(60.0°C)
InS
Ad
BOILER MINIMUM
SECTION C
The minimum allowed boiler target temperature and
boiler return protection temperature. Check the boiler
manufacturer’s manual for recommend supply water
temperatures.
120 to 225°F, OFF
(49.0 to 107.0°C, OFF)
Default = 200°F
(93.5°C)
Ad BOILER MAXIMUM SECTION C
The maximum allowed boiler target temperature.
0:00 to 3:00 min
Default = 0:10 min Ad
FIRE DELAY SECTION C
The time delay the control can expect between the
time that the relay contact closes to fire the boiler
and when the burner actually fires.
Adjust Menu (1 of 3)
The Adjust Menu items are the programmable settings
used to operate the mechanical equipment.
Continued on next page.
ADJUST MENU

© 2005 D420 - 06/05 8 of 24
Item Field Range Access Description
Au, 2 to 42°F
(Au, 1 to 23.5°C)
Default = Au
Ad
BOILER DIFFERENTIAL SECTION C
The temperature differential that the control is to use
when it is operating the boiler.
10 to 230 seconds
Default = 30 seconds Ad
BOILER MOTOR SECTION C
The amount of time required for the modulating
actuating motor to fully open the gas valve or operate
the fan speed from a stopped position to full speed
on a modulating boiler.
Note: This item is only available when the Boiler
On-Off /Mod DIP switch is set to Mod.
0 to 50%
Default = 0% Ad
MINIMUM MODULATION SECTION C
The minimum percent modulation of the burner.
Note: This item is only available when the Boiler
On-Off /Mod DIP switch is set to Mod.
50 to 100%
Default = 100% Ad
MAXIMUM MODULATION SECTION C
The maximum percent modulation of the burner.
Note: This item is only available when the Boiler
On-Off /Mod DIP switch is set to Mod.
Au, 5 to 30 min
Default = Au Ad
CYCLE LENGTH
The cycle length to which all tN4 devices will
synchronize.
OFF, Mb1, Mb2, Mb3,
Mb4
Default = OFF
InS
Ad
SCHEDULE
Selects which network setback schedule the control
will follow.
OFF,
1(parallel, no priority)
2(parallel, priority)
3(pri-sec, no priority)
4(Pri-sec, priority)
Default = 1
InS
Ad
DHW MODE SECTION F
Selects the DHW mode of operation. This determines
the operation of the primary pump in combination
with the DHW pump and whether or not DHW priority
is required.
100 to 220°F
(38.0 to 104.5°C)
Default = 180°F
(82.0°C)
Ad
DHW EXCHANGE OCCUPIED SECTION F
The minimum boiler target temperature to the DHW
heat exchanger during the Occupied period.
Note: This item is only available when DHW Mode is
set 1 through 4.
Adjust Menu (2 of 3)
Continued on next page.
ADJUST MENU

9 of 24 © 2005 D420 - 06/05
Item Field Range Access Description
OFF, ON
Default = OFF Ad
DHW EXCHANGE UNOCCUPIED SECTION F
Selects whether the control should respond to DHW
demands during the Unoccupied period. This item is
only available when DHW Mode is set 1 through 4 and
a network setback schedule is selected.
OFF,
1 (parallel, no priority)
2 (parallel, priority)
3 (pri-sec, no priority)
4 (Pri-sec, priority)
Default = 1
Ad
SETPOINT MODE SECTION H
Selects the Setpoint mode of operation. This
determines the operation of the primary pump.
60 to 220°F
(15.5 to 104.5°C)
Default = 180°F
(82.0°C)
Ad
SETPOINT OCCUPIED SECTION H
The minimum boiler target temperature when a
setpoint demand is present during the Occupied
period.
Note: This item is only available when Setpoint Mode
is set 1 through 4.
OFF, ON
Default = OFF Ad
SETPOINT UNOCCUPIED SECTION H
Selects whether or not a Setpoint demand will be
responded to during the UnOccupied period.
Note: This item is only available when Setpoint Mode
is set 1 through 4 and a network setback schedule
is selected.
40 to 100°F, OFF
(4.5 to 38.0°C, OFF)
Default = 70°F (21.0°C)
InS
Ad
WWSD OCCUPIED SECTION B
The system’s warm weather shut down temperature
during the Wake and Occupied periods.
40 to 100°F, OFF
(4.5 to 38.0°C, OFF)
Default = 60°F (15.5°C)
Ad
WWSD UNOCCUPIED SECTION B
The system’s warm weather shut down temperature
during the Sleep and Unoccupied period.
Note: This item is only available when the Schedule
is not set to OFF.
Adjust Menu (3 of 3)
ADJUST MENU
After the last item, the control returns to the first item in the menu.

© 2005 D420 - 06/05 10 of 24
Item Field Range Access Description
InS (Installer)
Ad (Advanced)
InS
Ad
ACCESS LEVEL
The access level that is to be used by the control.
Note: This item is only available when the Lock/Unlock
DIP switch is set to Unlock.
°F, °C
Default = °F
InS
Ad
UNITS
Select temperature units between Fahrenheit and
Celsius.
0 to 255 Ad
COMMUNICATION ERRORS
The number of tN4 communication errors that have
been recorded.
– – –, 1 to 24 Ad BOILER BUS DEVICES
Displays the number of devices on the boiler bus.
OFF, SEL Ad
FACTORY DEFAULT
Loads the factory defaults when the Up and Down
buttons are pressed.
420 InS
Ad
TYPE
Displays the type number of this product. The software
version is displayed when the Up button is held.
Misc (Miscellaneous) Menu (1 of 1)
The Miscellaneous Menu Items set control
and display options such as access level and
temperature units.
After the last item, the control returns to the first item in the menu.
MISC MENU

11 of 24 © 2005 D 420 - 06/05
Step 1 The primary pump turns on and remains on for
the rest of the test sequence.
Step 2 The boiler contact is closed to fire an on-off boiler
for 10 seconds or enable a modulating boiler.
IF the On-Off/Modulating DIP switch is set to Modulating
or the tekmar Stager/Off DIP switch is set to tekmar
Stager:
Step 3 When a demand is present, the modulation output
ramps up to 100%.
Step 4 When a demand is present, the modulation output
ramps down to 0%.
The boiler contact is opened and the boiler is
shut off.
Step 5 If DHW MODE is set to 1 or 2, the primary pump is
shut off and the DHW Pump contact is closed.
If DHW MODE is set to 3 or 4, the primary pump
stays on and the DHW Pump contact is closed.
The control exits the test sequence.
If a device fails to operate during the test sequence, refer
to the W420 Wiring Brochure to check the operation
of the control. If the control works properly, refer to any
troubleshooting information supplied by the equipment
manufacturer.
Testing the Control
The control has a built-in test routine that tests the main
control functions. The control continually monitors the
sensors and displays an error message whenever a fault
is found. The individual outputs and relays are tested using
a test sequence.
Test Sequence
Each step in the test sequence lasts 10 seconds.
•
• Start the test sequence by pressing the Test button.
•
• Pause the test sequence by pressing the Test button
again. To advance to the next step, press the Test button
again.
•
• If the test sequence is paused for more than five minutes,
the control exits the entire test routine.
•
• To advance to a particular step, repeatedly press and
release the Test button to display the appropriate
device.
Max Heat
The control has a function called Max Heat. In this mode, the
control turns on and operates the system up to the maximum
set temperatures as long as there is a demand for heat. tN4
thermostats operate to meet the occupied setting +5°F (3°C).
The control operates in this mode for up to 24 hours or until
the Test button is pressed. Use this mode to run the circulators
during system start-up to purge air from the piping.
To enable Max Heat:
1. Press and hold the Test button for 3 seconds. The control
flashes the MAX segment and displays the word OFF.
2. Using the Up or Down buttons, select the word On. After 3
seconds, the control turns on all outputs. However, the Max
Heat mode is still limited by the Boiler Maximum setting.
3. To cancel the Max Heat mode, press the Test button. Once
the Max Heat mode has either ended or is cancelled, the
control resumes normal operation.
Zone Test
In Zone Test mode, each tN4 device is individually turned
on one at a time. The control tests each zone for up to 5
minutes of no button activity. Use this feature to purge air
out of each zone and assist in troubleshooting.
To enable Zone Test:
1. Press and hold the Test button for more than 6 seconds.
The control displays ZN TEST OFF.
2. Press the Up button to change the display to ZN TEST ON.
After 3 seconds, the boiler and all pumps are shut off.
3. The control operates the tN4 device on the boiler bus and
the lowest device address. All other tN4 device zones
shut off. (Example: ZN TEST b:01 for the boiler bus and
device 1).
4. To change to the next device number, press the Up or
Down buttons. The previous zone turns off and the device
zone with the current address turns on.
5. To cancel the Zone Test, press the Test button. Once
the Zone Test ends or is cancelled, the control resumes
normal operation.
HAZARD
Access to the Test button requires the removal of the
front cover and exposes hazardous voltage while the
control is powered. Only trained, qualified and competent
personnel should operate the Test button.
Test Press and Hold
for 1 second
Test Press and Hold
for 3 seconds
HAZARD
Access to the Test button requires the removal of the
front cover and exposes hazardous voltage while the
control is powered. Only trained, qualified and competent
personnel should operate the Test button.
HAZARD
Access to the Test button requires the removal of the
front cover and exposes hazardous voltage while the
control is powered. Only trained, qualified and competent
personnel should operate the Test button.
Test Press and Hold
for 6 seconds

© 2005 D420 - 06/05 12 of 24
tekmarNet®4 Communication Section A
tekmarNet®4 (tN4) communicates between tN4 devices
(thermostats, Reset Module and Expansion Modules). Each
tN4 device is connected to a tN4 communication bus using
two wires. Each tN4 bus adjusts a single water temperature
in the system using indoor temperature feedback. The Boiler
Reset Module 420 allows for one tN4 bus. This allows you
to control a system with one water temperature.
A system that has more than one tN4 bus is referred to as
a tN4 network.
Outdoor Reset Module
The Boiler Reset Module 420 is the system control for a
hydronic heating system. The 420 operates a single heat
source such as a boiler, a domestic hot water tank, and
responds to other heating requirements such as pool heating
and snow melting. The 420 also coordinates and optimizes
the operation of all the tN4 thermostats.
tN4 Thermostat
The tN4 thermostat operates heating, cooling, and or
ventilation equipment for a zone. Several tN4 thermostats
may work in a group when operating a cooling system. Up
to 24 tN4 thermostats can connect to a single tN4 bus.
Outdoor Reset Section B
In a heating system, the rate of heat supplied to the
building must equal the rate of 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 is
defined by the characterized heating curve.
Characterized Heating Curves
A characterized heating curve determines the amount the
supply water temperature is raised for every 1° drop in
outdoor air temperature. There is a characterized heating
curve for each tN4 communication bus.
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.
Each tN4 bus is assigned a terminal unit setting that the
control uses to vary the supply water temperature to suit
to the terminal unit used. This improves the control of the
air temperature in the building.
Indoor Temperature Feedback
Most buildings have internal heat gains due to people,
passive solar heating and mechanical or electrical equipment.
Likewise, wind loads cause a building to lose heat faster than
during design conditions. If only the outdoor temperature is
measured, the control cannot compensate for these internal
heat gains or loses and the building may over or under heat.
In order to maintain the most comfortable temperature,
the control uses indoor temperature feedback from tN4
thermostats in order to adjust the water temperature on
each tN4 bus on a continual basis.
Sequence of Operation
DualZone Manager 337
ZoneA1
ZoneA2
Power
ZoneGroup Pump A
ZoneA3
ZoneB1
ZoneB2
ZoneB3
tN4
ZoneGroup Pump B
Bus 1 Bus 2
Network
tekmarNet®4
Thermostats tekmarNet®4 Thermostats
51 52 53 54 55 56 57 58 60 61 62 63 64
Boiler DHW Setpoint C
59
C Com Boil OutVlv
Demand Demand 24 V (ac) DHW
R
65
+
Mod(dc)
–
DHW Primary
10A
max.
66 67 68 69
N
Pump NPump
tN4
H7006B
BoilOn-Off / Mod
Off/ tekmar Stager
PoweredOutput1 VA
DHWValve:
24V (ac) 8 VA
Madein Canada
MeetsClass B: Canadian
ICES& FCC Part 15
Test
BoilerReset Module 420
Item
Menu
tektra991-01
Demands:20 - 260 V (ac)
RelayRating: 115V (ac) 5 A
/
Donot apply power

13 of 24 © 2005 D 420 - 06/05
Terminal Unit
There is a terminal unit setting for each tN4 bus. The
Terminal Unit setting is found in the Adjust menu.
Hydronic Radiant Floor (1)
Terminal type 1 is 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 (2)
Terminal type 2 is a light, or low mass, hydronic radiant
floor system. Most commonly, this type of radiant heating
system is either 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 (3)
Terminal type 3 is 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 (4)
Terminal type 4 is 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 (5)
Terminal type 5 is 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 (6)
Terminal type 6 is 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.
Outdoor Design Temperature
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.
The outdoor design setting is found in the Adjust menu.
Warm Weather Shut Down (WWSD)
The Warm Weather Shut Down is the outdoor temperature
at which hydronic heating is no longer required. The boiler
operates only when a Domestic Hot Water (DHW) Demand
or a Setpoint Demand is present.
The WWSD setting is found in the Adjust menu.

© 2005 D420 - 06/05 14 of 24
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 Boiler Terminal Unit setting
in the Adjust menu.
Terminal Unit BOIL DSGN BOIL MAX BOIL MIN
High Mass Radiant (1) 120°F (49°C) 140°F (60°C) OFF
Low Mass Radiant (2) 140°F (60°C) 160°F (71°C) OFF
Fancoil (3) 190°F (88°C) 210°F (99°C) 140°F (60°C)
Fin-Tube Convector (4) 180°F (82°C) 200°F (93°C) 140°F (60°C)
Radiator (5) 160°F (71°C) 180°F (82°C) 140°F (60°C)
Baseboard (6) 150°F (76°C) 170°F (77°C) 140°F (60°C)
Boiler Indoor Design
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.
•
• Locate the Boiler Indoor Design setting in the Adjust
menu.
Boiler Design Temperature
The boiler design supply temperature is the boiler water
temperature required to heat the zones on the typical
coldest day of the year.
•
• Locate the Boiler Design setting in the Adjust menu.
Boiler Characterized Heating Curve
Terminal Unit
Boiler
Design
Boiler
Indoor
Outdoor
Design
Decreasing Outdoor Temperatures
Increasing Water Temperatures
Boiler Temperature Control Section C
The 420 is able to operate a single, hot water, on-off or
modulating boiler as a heat source. For proper operation of
the boiler, the 420 must be the only control that determines
when the boiler is to fire.
*Important note: The boiler operator, also known as
an aquastat, remains in the burner circuit and acts as a
secondary upper limit on the boiler temperature. The boiler
operator temperature setting must be adjusted above the
420’s Boiler Maximum setting in order to prevent short
cycling of the boiler burner.
Boiler Target Temperature
The boiler target temperature is determined by connected
tN4 devices or by a DHW or Setpoint demand received by
the control. The tN4 devices determine the highest water
temperature required and then, requests 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
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. During this condition, if the boiler is
operating, the minimum segment is turned on in the display
when viewing either the boiler supply temperature or the
boiler target temperature. Set the Boiler Minimum setting
to the boiler manufacturer’s recommended temperature.
•
• Locate the Boiler Minimum setting in the Adjust menu.
Boil MIN + ½ Boiler Differential
Boil MIN
Boil MIN– ½ Boiler Differential
MIN segment on
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15 of 24 © 2005 D 420 - 06/05
Boiler Maximum
The boiler maximum is the highest temperature that the
control is allowed to use as a boiler target temperature. If
the control does target the Boiler Maximum setting, and the
boiler temperature is near the boiler maximum temperature,
the maximum segment will be displayed in the LCD while
either the boiler target temperature or the boiler temperature
is being viewed. At no time does the control operate the
boiler above 248°F (120.0°C).
•
• Locate the Boiler Maximum setting in the Adjust menu.
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Boil MIN + ½ Boiler Differential
Boil MAX
Boil MIN – ½ Boiler Differential
MAX
segment
on
MAX
segment
on
Fire Delay
The Fire Delay is the time delay that occurs between the
time that the control closes the boiler contact to fire the
boiler and when the burner fires.
•
• Locate the Fire Delay setting in the Adjust menu.
Boiler Contact Closed
Time
Fire Delay
Burner On
On-Off Boiler Operation
If the heat source is an On-Off Boiler, the Boil On-Off/Mod
DIP switch must be set to On-Off.
Differential
An on /off heat source must be operated with a differential
in order to prevent short cycling. With the control, either
a fixed or an auto differential may be selected. The boiler
differential is divided around the boiler target temperature.
The boiler contact closes when the supply water temperature
is 1/2 of the differential setting below the boiler target
temperature. As the supply temperature reaches 1/2 of
the differential above the boiler target temperature, the
boiler is shut off.
•
• Locate the Boiler Differential setting in the Adjust menu.
Differential = 10°F (6°C)
Target + ½ Differential
Target – ½ Differential
Target
165°F (74°C)
160°F (71°C)
155°F (68°C)
Boiler
On Boiler On
Fixed Differential
If the user desires to have a fixed differential, this is set
using the Boiler Differential setting in the Adjust menu.
Auto Differential
In order to decrease temperature swings and increase boiler
efficiency, the Auto Differential feature automatically changes
the on/ off differential of the boiler based on the heating
load. As the load increases, the differential will decrease
to minimize temperature swings. As the load decreases,
the differential will increase to prevent short cycling.
Off
Differential
Time
Heating Load
On
Modulating Boiler Operation
The 420 can operate a single hot-water modulating boiler.
This requires the use of the Mod (dc) output on the 420.
To operate a modulating boiler, the Boil On -Off/Mod DIP
switch must be set to Mod. The control operates the boiler
by first switching the boiler contact to allow the modulating
boiler to go through the ignition sequence (the boiler contact
may not be required on all modulating boilers). A 0-10 V (dc)
analog signal is used to modulate the boiler firing rate
from the Minimum Modulation setting using Proportional,
Integral and Derivative (PID) logic in order to satisfy the
boiler target temperature.
A modulating boiler requires all the same settings as an
on-off boiler in addition to the settings below.
Modulating Boiler Differential
A modulating boiler must be operated with a differential
while operating in low fire. The boiler differential is divided
around the boiler target temperature. The boiler burner
ignites at low fire when the supply water temperature is
1/2 of the Boiler Differential setting below the boiler target
temperature. The boiler is shut off in low fire as the supply
temperature reaches at least 1/2 of the differential above
the boiler target temperature. With the control, either a fixed
or an auto differential may be selected.
When the boiler is modulating above low fire, 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.

© 2005 D420 - 06/05 16 of 24
Boiler Motor Speed
The Boiler 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 open which can be found in the
manufacturer’s manual. The Boiler Motor Speed should
be set to this time.
The Boiler 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.
•
• Locate the Boiler Motor Speed setting in the Adjust menu.
Minimum Modulation
The minimum modulation defines the minimum output
signal from the control to the boiler burner. It is based on
a percentage of the control’s output signal range.
The Minimum Modulation default setting is 0%.
For boilers with electronic operators, the boiler’s input
signal range may not match the output signal range of
the 420 control. The Minimum Modulation setting limits
the control output range in order to match the boiler’s
input range.
•
• Locate the Minimum Modulation setting in the Adjust
menu.
To calculate the Minimum Modulation, use the following
formula:
For 0-10 V (dc):
Minimum Modulation =
0 V (dc) – Boiler’s Minimum Input Signal x 100%
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 420 control has an output signal range of
0- 10 V (dc).
To make the two signal ranges the same, the Minimum
Modulation required is:
Minimum Modulation = 0 V- 1.8 V x 100% = 18%
0 V- 10 V
1.8 V (dc)
10 V (dc)
Control Range Boiler Range
0 Vdc
18%
Maximum Modulation
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 default setting is 100%.
For boilers with electronic operators, the boiler’s input signal
range may not match the output signal range of the 420
control. The Maximum Modulation setting limits the control
output range in order to match the boiler’s input range.
•
• Locate the Maximum Modulation setting in the Adjust
menu.
To calculate the Maximum Modulation, use the following
formula:
For 0-10 V (dc):
Maximum Modulation =
0 V (dc) – Boiler’s Maximum Input Signal x 100%
0-10 V (dc)
Example:
A boiler’s input signal range is 2-9 V (dc). The 420 control
has an output signal range of 0- 10 V (dc).
To make the two signal ranges the same, the Maximum
Modulation required is:
Maximum Modulation = 0 V- 9 V x 100% = 90%
0 V- 10 V
10 V (dc)
Control Range Boiler Range
0 Vdc 0 V (dc)
2.0 V (dc)20%
90%

17 of 24 © 2005 D420 - 06/05
In some cases, multiple boilers may be required. In these
cases, the 420 allows for a connection to a tekmar Boiler
Control 264, 265, or 268. The 420 uses the modulating
output to provide a 0-10 V (dc) signal to the external input
terminals on the Boiler Control. The 420 controls the Boiler
Control target temperature by changing the voltage signal.
The Boiler Control responds to the boiler target by staging
the multiple boilers.
tekmar Stager Operation Section D
To use the tekmar Staging operation, the following DIP
switch settings are required:
1. Set the 420 Off/tekmar Stager DIP switch to tekmar
Stager.
2. Set the 420 Boil On-Off/Mod DIP switch to Mod.
The 420 boiler sensor must be located on the supply pipe
leading from the boilers. On the Boiler Control 264, 265, or
268, the External Input/Stand Alone DIP switch must be set
to External Input. Any domestic hot water (DHW) demands
or setpoint demands in the system must connect to the 420
in order to allow for DHW or setpoint priority.
Zone Load Shedding Section E
The control has a feature called zone load shedding. In
certain cases, the boiler may not have enough capacity
to satisfy all heating loads. In this case the control
prioritizes the heating loads and also prioritizes zones
in the following order:
First Priority: DHW and Setpoint loads while priority
is selected.
Second Priority: Boiler zones starting with network
address 1 up to 24.
Domestic Hot Water Temperature Operation Section F
DHW Demand
A powered DHW Demand is required in order for the control
to provide heat to the DHW system. A DHW aquastat or
setpoint control is used as a switch in the DHW demand
circuit. The control registers a DHW Demand when a
voltage between 24 and 230V(ac) is applied across the
DHW Demand terminals (53 and 54).
Once the control detects a DHW demand, the DHW Demand
segment turns on in the LCD.
Boiler Target Temperature
The boiler target temperature is at least as hot as the DHW
Exchange setting. The DHW demand overrides the boiler
reset target temperature, except when the boiler reset target
is higher than the DHW exchange setting.
•
• Locate the DHW Exchange setting in the Adjust menu.
DHW During UnOccupied
The control has a DHW Exchange UnOccupied setting that
allows the installer to select On or Off. When set to On, and
the control receives a DHW Demand during an UnOccupied
or Sleep period, the control continues operation of the DHW
system as it would during the Occupied and Wake periods.
When set to Off, the control can ignore a DHW Demand for
the duration of the UnOccupied and Sleep periods.
DHW Mode and Priority Operation
The control has four different settings available for DHW
Mode that affect pump operation. The required DHW Mode
setting will depend on the piping arrangement of the DHW
tank and whether or not priority for DHW is necessary. DHW
Priority stops or limits the delivery of heat to the building
heating system while the DHW tank calls for heat. This
allows for quick recovery of the DHW tank.
•
• Locate the DHW Mode setting in the Adjust menu.
DHW MODE 1 - DHW in Parallel no Priority
When a DHW Demand is present, the DHW Pump contact
closes. The primary pump (P1) does not turn on, but may
operate based on either Boiler or Mixing requirements or
a Setpoint Demand.
It is assumed that the DHW pump will provide adequate
flow through the heat exchanger and the boiler.
Mode = 1
DHW
Pump
Primary
Pump

© 2005 D420 - 06/05 18 of 24
DHW MODE 2 - DHW in Parallel with Priority
When a DHW Demand is present, the DHW Pump contact
closes. The primary pump (P1) can operate when a boiler
demand is present. If the boiler is unable to maintain the
boiler target temperature, space heating zones are shut
off sequentially using tN4 communication in order to
provide priority to the DHW tank. This is known as zone
load shedding.
It is assumed that the DHW pump will provide adequate
flow through the heat exchanger and the boiler.
DHW MODE 4 - DHW in Primary/Secondary with Priorit y
When a DHW Demand is present, the DHW Pump contact
is closed and the primary pump (P1) is operated. Priority
over space heating zones is achieved by shutting off the
zone pumps or zone valves through tN4 communication.
This is known as zone load shedding.
Mode = 2
DHW
Pump
Primary
Pump
OFF
Mode = 3
DHW
Pump
Primary
Pump
Mode = 4
OFF
DHW
Pump
Primary
Pump
DHW MODE 3 - DHW in Primary/Secondary no Priority
When a DHW Demand is present, the DHW Pump contact
is closed and the primary pump (P1) is operated.
that the control provides DHW priority is reduced. Once the
allowed time for priority has elapsed, the control overrides
the DHW priority and resumes space heating.
DHW Priority Override Time
Increasing Time
Decreasing Outdoor Air Temperature
Conditional DHW Priority
If the boiler supply temperature is maintained at or above the
required temperature during DHW generation, this indicates
that the boiler has enough capacity for DHW and possibly
heating as well. As long as the boiler supply temperature
is maintained near the target, DHW and heating occurs
simultaneously.
DHW Post Purge
After the DHW Demand is removed, the control performs
a purge on the boiler. The control shuts off the boiler and
continues to operate the DHW pump and the primary pump
(P1) if applicable. This purges the residual heat from the
boiler into the DHW tank. The control continues this purge
for a maximum of four minutes or until the boiler supply
water temperature drops 20°F (-6.5°C) below the boiler
target temperature during the DHW operation. The control
also stops the purge if the boiler supply temperature drops
below the current boiler target temperature.
DHW Mixing Purge
After DHW operation, the boiler is extremely hot. At the same
time, the heating zones may have cooled off considerably
after being off for a period of time. When restarting the
heating system after a DHW demand with priority, the control
shuts off the boiler and continues to operate the DHW pump
while the primary pump is turned on. This allows some of
the DHW return water to mix with the cool return water from
the zones and temper the boiler return water.
DHW
Pump
Primary
Pump
OFF
DHW Priority Override
DHW Priority Override applies to DHW MODE 2 and 4.
To prevent the building from cooling off too much or the
possibility of a potential freeze up during DHW priority, the
control limits the amount of time for DHW priority. As the
outdoor air temperature becomes colder, the length of time

19 of 24 © 2005 D420 - 06/05
DHW with Low Temperature Boilers Section G
If DHW heating is to be incorporated into a low temperature
system such as a radiant floor heating system, a mixing
device is often installed to isolate the high DHW supply
temperature from the lower system temperature. If a mixing
device is not installed, high temperature water could be
supplied to the low temperature system while trying to
satisfy the DHW demand. This may result in damage to
the low temperature heating system.
The control is capable of providing DHW heating in such a
system while minimizing the chance that the temperature
in the heating system exceeds the design supply water
temperature. In order to do this, the control must be set
to DHW MODE 2 or DHW MODE 4 and Boil MIN must be
set to OFF.
On a call for DHW, the control provides DHW priority by
sending a message on the boiler temperature bus to the tN4
thermostats to shut off the heating zones for a period of time.
The length of time is based on the outdoor air temperature
as described in the DHW Priority Override section. However,
if the DHW Demand is not satisfied within the allotted time,
the boiler shuts off and the heat of the boiler is purged into
the DHW tank. A DHW mixing purge occurs in order to
reduce the boiler water temperature and once the boiler
supply temperature is sufficiently reduced, the DHW Pump
contact shuts off. The heating system zones are allowed
to turn on for a period of time to prevent the building from
cooling off. After a period of heating, and if the DHW Demand
is still present, the control shuts off the heating system and
provides heat to the DHW tank once again.
Setpoint Temperature Operation Section H
Setpoint
The control can operate to satisfy the requirements of a
setpoint load in addition to a space heating load and a
DHW load. A setpoint load overrides the current outdoor
reset temperature and WWSD setting in order to provide
heat to the setpoint load.
Setpoint Demand
A Setpoint Demand is required in order for the control to
provide heat to a setpoint load.
The control registers a setpoint demand when a voltage
between 24 and 230 V (ac) is applied across the Setpoint
Demand terminals (55 and 56). Once voltage is applied,
the Setpoint Demand segment turns on in the LCD.
Boiler Target During Setpoint
The boiler target temperature during a Setpoint Demand is
increased to at least the Setpoint setting. This temperature is
maintained as long as the control has a setpoint demand.
Setpoint During UnOccupied
The control has a Setpoint UnOccupied setting that allows
the installer to select On or Off. When set to On, and the
control receives a Setpoint Demand during an UnOccupied or
Sleep period, the control continues operation of the Setpoint
system as it would during Occupied and Wake periods. When
set to Off, the control can ignore a Setpoint Demand for the
duration of the UnOccupied and Sleep periods.
Setpoint Modes
The Setpoint Mode determines the operation of the primary
pump. The Setpoint Mode setting is found in the Adjust
menu.
Setpoint Mode 1 - Setpoint in Parallel
Whenever a setpoint demand is present, the boiler is
operated to maintain the setpoint target. The primary pump
(P1) does not turn on, but may operate based on either a
Boiler, Mixing or a DHW Demand.
It is assumed that the Setpoint pump will provide adequate
flow through the heat exchanger and the boiler.
Primary
Pump
Setpoint
Mode = 1
Setpoint Mode 2 - Setpoint in Parallel with Priority
When a Setpoint Demand is present, the boiler is operated
to maintain the setpoint target. The primary pump (P1) can
operate when a boiler demand is present. If the boiler is
unable to maintain the boiler target temperature, space heating
zones are shut off sequentially using tN4 communication in
order to provide priority for the setpoint load. This is known
as zone load shedding.
It is assumed that the setpoint pump will provide adequate
flow through the heat exchanger and the boiler.
Setpoint
Primary
Pump
OFF
Mode = 2

© 2005 D420 - 06/05 20 of 24
Setpoint Mode 3 – Setpoint in Primary /Secondary
Whenever a setpoint demand is present, the primary pump
(P1) is turned on and the boiler is operated to maintain the
setpoint target.
Setpoint Mode 4 - Setpoint in Primary /Secondary with
Priority
Whenever a Setpoint Demand is present, the primary pump
(P1) is turned on and the boiler is operated to maintain the
setpoint target. Space heating zones will be shut off using
zone load shedding if the boiler is unable to maintain the
boiler target temperature.
Primary
Pump
Setpoint
Mode = 3
Setpoint
Primary
Pump
OFF
Mode = 4
Setpoint Priority Override
Setpoint Priority Override applies to SETPOINT MODE
2 and MODE 4. To prevent the building from cooling off
too much or the possibility of a potential freeze up during
setpoint priority, the control limits the amount of time for
setpoint priority. As the outdoor air temperature becomes
colder, the length of time the control provides setpoint
priority is reduced. Once the allowed time for priority has
elapsed, the control overrides the setpoint priority and
resumes space heating.
Conditional Setpoint Priority
If the boiler supply temperature is maintained at or above
the required temperature during setpoint generation, this
indicates that the boiler has enough capacity for setpoint
and possibly heating as well. As long as the boiler target
temperature is maintained, setpoint and heating occur at
the same time.
Pump Operation Section I
Primary Pump P1
The primary pump P1 is switched on in the following
situations:
•
• There is a Boiler Demand.
•
• There is a DHW Demand and the control is set to DHW
Mode 3 or 4.
•
• The control is completing a DHW Purge.
•
• There is a Setpoint Demand and the control is set to
Setpoint Mode 3 or Mode 4.
DHW Pump
The DHW Pump operates whenever there is a DHW Demand
and the control is not in DHW Priority Override.
DHW Valve
The DHW Valve operates whenever there is a DHW Demand
and the control is not in DHW Priority Override.
Primary
Pump
DHW
Pump