Bosch Buderus SSB399 Use and maintenance manual

Bosch Buderus SSB Boiler Control Operations
SSB255 | SSB399 | SSB512
Control Operations Guide
WARNING:
the heating system can cause personal injury and property damage.
Follow these instructions precisely.
If you require assistance or further information, contact a licensed

2 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
03.2018 |Bosch Thermotechnology Corp.
Data subject to change

Control Operations Guide Bosch Buderus SSB255 | SSB399 | SSB512 Boilers | 3
Bosch Thermotechnology Corp. |03.2018 Data subject to change
Table of Contents
1 Key to Symbols and Safety Instructions 4
1.1 Key to symbols 4
1.2 Safety 4
2 Boiler Settings Menu 5
3 Heating Modes 6
3.1 Central heating (CH) mode 6
4 General Operation Settings 12
5 Outdoor Reset Curve Settings 14
6 Domestic Hot Water 16
6.1 Domestic hot water settings 16
6.2 Domestic hot water operation 17
7 Cascade Operation 18
7.1 Cascade operation settings 18
7.2 Cascade operation - set-up of boilers 20
7.3 Cascade - start sequence 22
7.4 Cascade - stop sequence 22
8 Start-up & Commissioning Settings 23
9 Cascade Quick Set-Up 24

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1 Key to Symbols and Safety Instructions
1.1 Key to symbols
Warnings
Warnings in this document are identified by a
warning triangle printed against a grey background.
Keywords at the start of a warning indicate the type and seriousness
of the ensuing risk if measures to prevent the risk are not taken.
The following keywords are defined and can be used in this document:
DANGER indicates a hazardous situation which, if not avoided, will result
in death or serious injury.
WARNING indicates a hazardous situation which, if not avoided, could
result in death or serious injury.
CAUTION indicates a hazardous situation which, if not avoided, could
result in minor to moderate injury.
NOTICE is used to address practices not related to personal injury.
Important information
This symbol indicates important information where
there is no risk to people or property.
1.2 Safety
Please read safety precautions before installation
WARNING:
Improper installation, set-up, modification, operation or
maintenance of the heating system can cause personal injury
and property damage.
Follow these instructions precisely.
If you require assistance or further information, contact a
licensed contractor / gas fitter.

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2 Boiler Settings Menu
Function Parameter Description
General Operation
1 Central Heating (CH) Mode
2 Pump Mode
3 CH Setpoint
4 System Pump Overrun
5 Boiler Pump Overrun
7 Central Heating Hysteresis (Differential)
9 Anti Cycle Period
10 Anti Cycle Temperature Differential
11 Ramp Delay Step Modulation
14 Maximum Power Central Heating
15 Minimum Power Central Heating / DHW
Outdoor Reset Curve
19 Design Supply Temperature
20 Design Outdoor Temperature
21 Baseline Supply Temperature
22 Baseline Outdoor Temperature
23 Design Supply Minimum Limit
24 Design Supply Maximum Limit
25 Warm Weather Shutdown
26 Boost Temperature Increment
27 Boost Time Delay
28 Night Setback Temperature
29 Weather Setpoint
Domestic Hot Water
35 Domestic Hot Water Mode
36 Domestic Hot Water Tank Differential DOWN
37 Domestic Hot Water Tank Differential UP
38 Domestic Hot Water Tank Supply Extra
42 Domestic Hot Water Priority
43 Domestic Hot Water Priority Time
44 Domestic Hot Water Pump Overrun
48 Domestic Hot Water Tank Setpoint
Cascade Operation
72 Permit Emergency Mode
73 Boiler Address
74 Emergency Setpoint
75 Delay Period Start Next Boiler
76 Delay Period Stop Next Boiler
77 Differential DOWN Start Boiler
78 Differential UP Stop Boiler
79 Maximum Setpoint Offset DOWN
80 Maximum Setpoint Offset UP
81 Start Modulation Delay Factor
82 Next Boiler START Rate
83 Next Boiler STOP Rate
84 Boiler Rotation Intervale
85 Domestic Hot Water Boiler Assign
Start-up & Commisioning
89 Frost Protection
90 Frost Protection Setpoint
91 Domestic Hot Water Maximum Limit
92 Fan Speed Maximum
93 Fan Speed Minimum
94 Fan Speed Ignition
97 Appliance Model
98 Gas Type
99 Flue Length Range
Table 1

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Data subject to change
3 Heating Modes
3.1 Central heating (CH) mode
There are 6 onboard CH Mode settings which may be selected with the SSB Boiler.
1. CH Mode = “0” [default mode] Setpoint control of the boiler using dry
contacts (TT)
2. CH Mode = “1” Outdoor Reset using ON/OFF control of the boiler using dry
contacts (TT)
3. CH Mode = “2” Full Outdoor reset with no heat demand
4. CH Mode = “3” Permanent Setpoint Demand
5. CH Mode = “4” Analog control (0-10Vdc) of set point temperature
6. CH Mode = “5” Analog control (0-10Vdc) of Boiler Power (%)
Central Heating Mode 0 [default mode]
(Setpoint control of the boiler using dry contacts #11 and #12)
CH Mode “0” - Boiler demand is generated thru a call for heat on low voltage contacts
#11 and #12 (dry contacts only). The Boiler will then target a temperature equal to
“CH Setpoint” (par.#3) at the Supply Temperature Sensor. If Temperature exceeds
the target Setpoint temperature by “CH Hysteresis” (par.#7) the burner will shut off
until the Supply Temperature Sensor drops the value of “CH Hysteresis” below the
target Setpoint Temperature.
Example:
If “CH Setpoint” is set for 140°F and CH Hysteresis is set for 10°F and there is a call
for heat on #11 and #12 the burner will start when the Boiler Supply Temperature
(System Supply Temperature sensor for cascade) reads a temperture of 130°F or less
and will remain operating until the call for heat is satisified or until the sensor reads
a temperature of 150°F or greater. As long as the call for heat remains the Boiler and
CH Pump contacts will remain energized. The Burner will remain off until temperature
falls to 130°F.
Central Heating
(CH)Mode Description Set these Parameters
Parameter # Description Default Range
CH Mode = “0” Setpoint control using dry
contacts (TT)
3 CH Setpoint 176°F 68 - 194°F
4 System pump overrun 300 sec. 0 – 900 sec.
5 Boiler pump overrun 300 sec. 0 – 900 sec.
7 CH Hysteresis 5.4°F 0 - 36°F
9 Anti-cycle period 180 sec. 10 – 900 sec.
10 Anti-cycle Temp Diff 12.6°F 0 - 36°F
23 Design Supply Min 68°F 39.2 – 179.6°F
24 Design Supply Max. 194°F 80.6 - 194°F
Table 2

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Central Heating Mode 1
(On/Off with Outdoor Reset using dry contacts #11 and #12)
CH Mode “1” - Boiler demand is generated thru a call for heat on low voltage
contacts #11 and #12 (dry contacts only). Boiler will target a system supply water
temperature equal to the corresponding point on the installer programmed heating
curve. (See page 7 for details on how-to program the heating curve). If the System
Temperature sensor exceeds the calculated heating curve temperature by “CH
Hysteresis” (par.#7) the burner will shut off until the System Temperature sensor
reads “CH Hysteresis” below the target Setpoint Temperature.
Example:
Based on the heating curve programmed by the installer, the calculated supply water
temperature on a 32°F degree day outside corresponds with a target boiler water
temperature of 140°F. If CH Hysteresis is set for 10°F, and there is a call for heat
on #11 and #12, then the burner will turn on when the Boiler Supply Temperature
sensor (System Supply Temperature sensor for cascade) reads a temperture of
130°F or less and will remain operating until the call for heat is satisified or until the
sensor reads a temperature of 150°F or greater. As long as the call for heat remains
the Boiler and CH Pump contacts will remain energized. The Burner will remain off
until temperature measured at the system supply sensor falls to 130°F
Central Heating
(CH)Mode Description Set these Parameters
Parameter # Description Default Range
CH Mode = “1” On/Off with reset water
temperature
19 Design Supply °F 176°F 68 - 194°F
20 Design Outdoor °F 24.8°F -13 - 77°F
21 Baseline Supply °F 104°F 68 - 194°F
22 Baseline Outdoor °F 69.8°F 35.6 - 86°F
23 Design Supply min 68°F 39.2 – 179.6°F
24 Design Supply max 194°F 80.6 - 194°F
25 WWSD 69.8°F 35.6 - 95°F
26 Boost Temp Incr. 0°F 0 - 54°F
27 Boost Temp Delay 20 min. 1 – 120 min.
Table 3

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Data subject to change
Central Heating Mode 2
(Full Outdoor reset with no heat demand)
CH Mode“2” - Boiler demand is generated when the outdoor temperature falls
below the value of “Weather Setpoint” (par.#29). When this occurs the Boiler and
CH pump contacts are energized and the Boiler will target a system supply water
temperature corresponding to a point on the installer programmed heating curve.
(See “How to Program the Heating Curve” for details). If the System Temperature
sensor exceeds the calculated heating curve temperature by “CH Hysteresis”
(par.#7) the burner will shut off until the System Temperature sensor reads “CH
Hysteresis” below the target Setpoint Temperature. This CH Mode is for constant
circulation applications. The Boiler and CH pump contacts will remain energized
as long as the outdoor temperature is less than the value of “Weather Setpoint”
(par.#29). Using the low voltage contacts #11 and #12 it is possible to apply a
set-back to the heating curve. “Night Setback Dif” (par.# 28) controls the parallel
temperature shift that is applied to the curve when #11 and #12 contacts are
“closed” using a clock or switch.
Example:
“Weather Setpoint” is programmed for 60°F. The outdoor temperature falls below
this value. The boiler energizes Boiler and CH pump contacts. Based on the heating
curve programmed by the installer in this application, the calculated supply water
temperature on this particular temperature day corresponds to a target boiler
water temperature of 140°F. If CH Hysteresis is set for 10°F, and and the outdoor
temperature remains below the value of “Weather Setpoint”, then the burner will turn
on when the Boiler Supply Temperature sensor (System Supply Temperature sensor
for cascade) reads a temperature of 130°F or less and will remain operating until
the outdoor temperature exceeds the value of “Weather Setpoint” or if the sensor
reads a temperature of 150°F or greater. As long as the outdoor temperature remains
below the value of “Weather Setpoint” the Boiler and CH Pump contacts will remain
energized. The burner will remain off until the system supply temperature falls to
130°F.
Central Heating
(CH)Mode Description Set these Parameters
Parameter # Description Default Range
CH Mode = “2” Full Outdoor reset
with no heat demand
19 Design Supply °F 176°F 68 - 194°F
20 Design Outdoor °F 24.8°F -13 - 77°F
21 Baseline Supply °F 104°F 68 - 194°F
22 Baseline Outdoor °F 69.8°F 35.6 - 86°F
23 Design Supply min 68°F 39.2 – 179.6°F
24 Design Supply max 194°F 80.6 - 194°F
25 WWSD 69.8°F 35.6 - 95°F
26 Boost Temp Incr. 0°F 0 - 54°F
27 Boost Temp Delay 20 min. 1 – 120 min.
28 Night Setback 18°F 0 - 90°F
29 Weather Setpoint 68°F 32 - 122°F
Table 4

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Central Heating Mode 3
(Permanent set point demand)
CH Mode“3” - Boiler demand is always “ON” in CH Mode 3 – “Permanent Demand
Mode”. In this mode the Boiler and CH Pump contacts will always be energized. When
the Supply Temperature Sensor falls below the value of “CH Setpoint” (par.#3)
minus the value of “CH Hysteresis” (par.#7), the burner will turn on. The burner
will remain on as long as the supply temperature remains below the value of “CH
Setpoint” plus “CH Hysteresis”. Using the low voltage contacts #11 and #12 it is
possible to apply a set-back to the “CH Setpoint” target temperature. “Night Setback
Dif” (par.# 28) controls the temperature shift that is applied to the “CH Setpoint”
when #11 and #12 contacts are “closed” using a clock or switch.
Example:
With both Boiler and CH Pump contacts energized, the boiler will monitor the Supply
Temperature Sensor. The application calls for a setpoint of 140°F with and Hysteresis
setting of 10°F. When the temperature of the Boiler Supply Temperature sensor
(System Supply Temperature sensor for cascade) falls below 130°F ( the value of
“CH Setpoint” minus “CH Hysteresis”) the burners will turn on. Burners will remain
on as long as the sensor does not exceed 150°F ( the value of “CH Setpoint” plus
“CH Hysteresis”). In the evening the application calls for a reduced supply water
temperature of 120°F. A timer/clock is installed and wired to contacts #11 and #12
of the boiler and these contacts are “closed” between the hours of 10 pm and 5 am.
During that time period the “CH Setpoint” is reduced by the value programmed into
“Night Setback Dif”. In this example the value is set for 20°F.
Central Heating
(CH)Mode Description Set these Parameters
Parameter # Description Default Range
CH Mode = “3”
Permanent
Setpoint
Demand
3 CH Setpoint 176°F 68 - 194°F
4 System pump overrun 300 sec. 0 – 900 sec.
5 Boiler pump overrun 300 sec. 0 – 900 sec.
7 CH Hysteresis 5.4°F
9 Anti-cycle period 180 sec. 10 – 900 sec.
10 Anti-cycle Temp Diff 12.6°F 0 - 36°F
24 Setpoint Max. 194°F 80.6 - 194°F
28 Night Setback 18°F 0 - 90°F
Table 5

10 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
03.2018 |Bosch Thermotechnology Corp.
Data subject to change
Central Heating Mode 4
(Analog 0-10 Vdc Setpoint Control)
CH Mode“4” - Boiler demand is generated by a 0-10 Vdc analog signal from a
Building Management System (BMS). An initial heat request is generated via a
signal of 1.5 VDC or greater. Boiler modulation between “Design Supply Min”
(par.#23) and “Design Supply Max” (par.#24) will occur between 2 and 10 Vdc.
When a demand voltage of 1.5 VDC or greater is applied the Boiler and CH pump
contacts are energized and the Boiler will target a system supply water temperature
corresponding to the appropriate setpoint temperature based upon the voltage signal
and the minimum and maximum setpoint settings. If the Boiler Supply Temperature
sensor (System Supply Temperature sensor for cascade) exceeds the targeted
setpoint plus “CH Hysteresis” (par.#7) the burner will shut off until the sensor reads
“CH Hysteresis” below the targeted Setpoint Temperature. Once the initial demand
has occurred The Boiler and CH pump contacts will remain energized as long as the
voltage from the BMS remains greater than 1 VDC.
Figure 1
OFF
1.0 1.5 2.0
ON
9
Modulation
CH Setpoint Max
CH Setpoint Min
Voltage (Vdc)
Set Point F°
Central Heating
(CH)Mode Description Set these Parameters
Parameter # Description Default Range
CH Mode = “4” Analog 0-10 VDC
Setpoint Control
4 System pump overrun 300 sec. 0 – 900 sec.
5 Boiler pump overrun 300 sec. 0 – 900 sec.
7 CH Hysteresis 5.4°F 0 - 36°F
9 Anti-cycle period 180 sec. 10 – 900 sec.
10 Anti-cycle Temp Diff 12.6°F 0 - 36°F
23 Design Supply Min 68°F 39.2 – 179.6°F
24 Design Supply Max. 194°F 80.6 - 194°F
Table 6

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Bosch Thermotechnology Corp. |03.2018 Data subject to change
Central Heating Mode 5
(Analog 0-10 Vdc Power % Modulation)
CH Mode“5” - Boiler demand is generated by a 0-10 VDC analog signal from a
Building Management System (BMS). An initial heat request is generated via a signal
of 1.5 VDC or greater. Boiler modulation between “Minimum Power” (par.#15) and
“Maximum Power” (par.#14) will occur between 2 and 10 VDC. When a demand
voltage of 1.5 VDC or greater is applied the Boiler and CH pump contacts are
energized and the Boiler will operate at the corresponding Power %. The Power % will
be based upon the voltage signal and scaled between the Minimum and Maximum
power settings. Once the initial demand has occurred The Boiler and CH pump
contacts will remain energized as long as the voltage from the BMS remains greater
than 1 VDC.
Figure 2
OFF
1.0 1.5 2.0
ON
9
Voltage (VDC)
Max Power
Min Power
Modulation
Power (%)
Central Heating
(CH)Mode Description Set these Parameters
Parameter # Description Default Range
CH Mode = “5” Analog 0-10 VDC
Power Modulation
4 System pump overrun 300 sec. 0 – 900 sec.
5 Boiler pump overrun 300 sec. 0 – 900 sec.
7 CH Hysteresis 5.4°F 0 - 36°F
9 Anti-cycle period 180 sec. 10 – 900 sec.
10 Anti-cycle Temp Diff 12.6°F 0 - 36°F
14 Max Power CH 100 % 50 – 100 %
15 Min Power CH/DHW 1% 1 – 30%
24 Design Supply Max. 194°F 80.6 - 194°F
Table 7

12 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
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Data subject to change
4 General Operation Settings
Parameter Description
CH Mode
(parameter #1)
Set Central Heating (CH) Mode based upon the desired control strategy for the boiler. See pages 2 thru 7 of this
manual for a detailed explanation of each CH Mode.
Pump Mode
(parameter #2)
Three different pump modes may be selected for the boiler depending upon how the boiler is piped and how many
pumps are controlled by the boiler. Diagrams (Fig. 3,4,5) for the three different pump modes are shown on the
following page.
CH Setpoint
(parameter #3)
Central Heating Setpoint only applies to CH Mode #0 ( On/Off using dry contacts) and CH Mode #3 (Permanent
set point demand). The value set for CH Setpoint will be the boiler supply water temperature (system supply for
cascade).
System Pump Overrun
(parameter #4)
The amount of time in seconds the CH Pump contacts (#104 thru #106) will be energized after the demand
for heat has ended. Default is 300 seconds (5 minutes). The parameter is adjustable from 0 seconds to 900
seconds in 10 second increments.
Boiler Pump Overrun
(parameter #5)
The amount of time in seconds the Boiler Pump contacts (#101 thru #103) will be energized after the demand for
heat has ended. Default is 300 seconds (5 minutes). The parameter is adjustable from 0 seconds to 900 seconds in
10 second increments.
CH Hysteresis
(parameter #7)
The temperature differential used by the boiler to control the on/off function of the burner. The Central Heating
Differential applies to all CH Modes. If the target boiler supply sensor (system supply for cascade) registers a
temperature above the target by more than the value of the differential, the burner will turn off. The burner will not
turn on until the boiler supply (system supply for cascade) sensor value has fallen the same amount equal to the
differential below the target setpoint temperature.
Anti Cycle Period
(parameter #9)
The amount of time in seconds the boiler will wait before restarting. The parameter is adjustable from 10 seconds to
900 seconds in 10 second increments
Anti Cycle Temp. Difference
(parameter #10)
In addition to the Anti Cycle Period (see above) the boiler will monitor the System Supply Temperature Sensor. If the
Anti Cycle Period is active and there is a pending call for heat, the Anti Cycle Period will be overriden, and the burner
will fire, if the temperature at the Supply sensor drops a certain number of degrees prior to completing the Anti Cycle
Period. Default value for this parameter is 12.6°F. The parameter is adjustable from 0°F to 36°F.
Ramp Delay Step Mod.
(parameter #11)
Default setting for this parameter is “Disabled” but can be set to “Enabled”. By enabling this parameter the boiler
follows a pre-defined set of modulation “steps”. The boiler will begin operating at a 10% power level after ignition for
60 seconds. Once this time period has passed, should there still be a call for heat from the system, the boiler power
level will be increased +20%. Every 30 seconds thereafter the boiler power will be increased by an additional +20%
until the call for heat is either satisfied, or the boiler reaches the CH Setpoint (par.#3) + Hysteresis (par.#7), or the
boiler reaches 100% of it’s maximum power level.
Max. Power Central Heating
(parameter #14)
The Maximum burner power for Central Heating can be limited during operation. Default value is 100% and may be
adjusted down in 1% increments to 50%.
Min. Power Central Heating/DHW
(parameter #15)
The Minimum burner power for Central Heating and DHW operation can be limited during operation. Default value is
1% power and may be adjusted up in 1% increments to 30%.
Table 8

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Bosch Thermotechnology Corp. |03.2018 Data subject to change
Figure 3
Pump mode = 2 (default) Boiler with a manifold and two pump circuits CH/DHW
DHW_mode=1DHW_mode=0 (Ch only)
CH
return
CH supply
Primary
Heat Exchanger
T_flue
CH PUMP
Manifold
T_supply
Safety Limit
GENERAL
PUMP
N
LJ6-1
J6-3
J7-5
J6-2
DHW
PUMP
CH /SYSTEM
PUMP
L
N
L
J7-2
GENERAL
PUMP
J7-1 PE
CH return
CH supply
GENERAL
PUMP
Manifold
in
DHW
CH
PUMP
T_store
DHW
PUMP
out
Primary
Heat Exchanger
Figure 4
Pump mode = 0 Boiler with two pump circuits Ch/DHW (move the internal pump wiring to the CH terminal)
DHW
PUMP
T_store
CH supply
out in
DHW
CH return
CH
PUMP
Primary
Heat Exchanger
DHW_mode=1
DHW
PUMP
DHW_stat
CH supply
out in
DHW
CH return
CH
PUMP
Primary
Heat Exchanger
DHW_mode=2
CH supply CH return
CH
PUMP
T_return
T_flue
T_supply
Safety Limit
Primary
Heat Exchanger
DHW_mode=0 (Ch only)
CHW
PUMP
L
J6-1
J6-3
J6-2
J7-1
N
L
PE
Figure 5
Pump mode = 1 Boiler with one primary pump and 3-way valve for DHW (move the internal pump wiring to the CH terminal)
3-WAY
VALVE
T_store
CH supply
out in
DHW
CH return
GENERAL
PUMP
Primary
Heat Exchanger
DHW_mode=1
3-WAY
VALVE
DHW_stat
CH supply
out in
DHW
CH return
BOILER
PUMP
Primary
Heat Exchanger
DHW_mode=2
CH supply CH return
GENERAL
PUMP
T_return
T_flue
T_supply
Safety Limit
Primary
Heat Exchanger
DHW_mode=0 (Ch only)

14 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
03.2018 |Bosch Thermotechnology Corp.
Data subject to change
5 Outdoor Reset Curve Settings
Parameter Description
Design Supply Temperature
(parameter #19) The water temperature the boiler will supply at Design Outdoor temperature
Design Outdoor Temperature
(parameter#20) The outdoor air temperature at which the boiler will supply the Design supply water temperature
Baseline Supply Temperature
(parameter#21) The water temperature the boiler will supply at the Baseline Outdoor temperature.
Baseline Outdoor Temperature
(parameter#22) The outdoor air temperature at which the boiler will target the Baseline Supply Temperature.
Design Supply Minimum Limit
(parameter#23)
The minimum supply water temperature the heating system will provide to the system. May be the same value as
Parameter #21
Design Supply Maximum Limit
(parameter#24)
The maximum supply water temperature the heating system will provide to the system. May be the same value as
Parameter #19
"Warm Weather Shutdown
(parameter #25)
The temperature above which heating is no longer necessary. All calls for heat will be ignored as long as the outdoor
temperature remains above the Warm Weather Shutdown value.
Table 9
Figure 6
Design Supply Temp
(par. #19)
Design Supply
Min Limit
(par. #25)
Boiler Supply Temperature ºF
Outdoor Air Temperature
Baseline Supply Temp
(par. #21)
Design Supply
Max Limit
(par. #24)
Design Outdoor Temp
(par. #20)
Baseline Outdoor Temp
(par. #22)
(par. #23)

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Bosch Thermotechnology Corp. |03.2018 Data subject to change
Parameter Description
Boost Temp Increment
(parameter #26)
Boost Temp Increment is active for CH Modes 1. If a call for heat has not been satisfied within the period of time
defined within Boost Time Delay (see below) the targeted supply temperature will be increased by the value of Boost
Temp increment. This process of Boosting supply water will continue until the call for heat is satisified. The default
value for this parameter is 0°F. The parameter is adjustable from 0°F to 54°F.
Boost Time Delay
(parameter #27)
Boost Time Delay is active only for CH Modes 1. If a call for heat has not been satisfied within the time limit (in
minutes) defined within Boost Time Delay, the boiler supply water temperature will be increased by Boost Temp
Increment (see above). The default value for this parameter is 20 minutes. The parameter is adjustable from 1 to
120 minutes.
Night Setback Temp.
(parameter #28)
Only available for CH Modes #2 and #3. The value the heating curve will be reset as long as contacts #11 & #12
are “closed” (i.e. via an external clock timer or switch). Default value is 18°F. The parameter is adjustable from 0 to
90°F.
Weather Setpoint
(parameter #29)
Weather Setpoint is only active for CH Modes #2 (full outdoor reset with no heat demand). When the outside
temperature falls below the value set for Weather Setpoint, a heating demand is generated and the boiler will begin
to operate. Boiler operation will continue until the outdoor temperature rises above the value set for warm weather
shutdown
Table 10

16 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
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Data subject to change
6 Domestic Hot Water
6.1 Domestic hot water settings
Parameter Description
DHW Mode
(parameter #35)
When an Indirect tank is present in the system set DHW Mode to “1” when using the factory supplied 10K ohm
sensor or set to “2” if using a third-party aquastat. Default value is “0” (Off).
DHW Tank Hyst. Down
(parameter #36)
The necessary temperature drop of the indirect tank temperature needed before the boiler will begin to recover the
tank. Only active when DHW Mode (par. #35) is set to “1” and a 10k ohm sensor is used. Default value is 7.2°F.
Adjustable between 36°F. Only applies to systems using a 10k ohm thermistor (Parameter #35 DHW Mode = “1”)
DHW Tank Hyst. Up
(parameter #37)
The necessary temperature overshoot of the indirect tank temperature needed before the boiler will stop heating
the indirect tank. Default value is 0°F. Adjustable between 0°F and 36°F. Only applies to systems using a 10k ohm
thermistor (Parameter #35 DHW Mode = “1”)
DHW Tank Supply Extra
(parameter #38)
The Target Supply Water temperature to the indirect coil is equal to DHW Tank Setpoint (par. #48) + DHW Tank
Supply Extra.
DHW Priority
(parameter #42)
Default setting is “0” - Timed DHW Priority. Timer starts when there is both a DHW and a call for heat. See DHW
Priority Time (par. #43) for adjusting the length of time priority is given over a call for heat. Setting a value of “1”
gives DHW unlimited priority over a call for heat. Setting the value to “2” gives a call for heat unlimited priority over a
call for domestic hot water
DHW Max Priority Time
(parameter #43) Default DHW priority [see DHW Priority (par.#42)] time is 30 minutes Adjustable from 1 to 255 minutes.
DHW Pump Overrun
(parameter #44)
Length of time the DHW pump contacts remain energized after a call for DHW has ended. Default setting is 15
seconds. Adjustable between 0 and 255 seconds.
DHW Tank Setpoint
(parameter #48) Target temperature of the indirect tank. Default value is 120°F. Adjustable between 104°F and 140°F.
Table 11

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Bosch Thermotechnology Corp. |03.2018 Data subject to change
6.2 Domestic hot water operation
The SSB Boiler onboard control can support domestic hot water production using an
indirect tank. The boiler can use either the supplied 10K ohm domestic sensor or a
aquastat (dry contact only, aquastat supplied by installer) to control the heating of
an indirect tank. The 10k ohm sensor or aquastat are wired to the #9 and #10 low
voltage terminal block of the SSB boiler. Parameter #35 (Domestic Hot Water Mode)
must be set to the appropriate value depending upon which type of sensor is used.
Follow the instructions below for the sensor type you have chosen to use with the
SSB Boiler.
Using the supplied 10k ohm Sensor:
1. Wire 10k ohm sensor to low voltage terminals #9 and #10 on the boilers
main control panel.
2. Within the “Boiler Settings” menu set Parameter #35 to “1”.
3. Set desired domestic hot water temperature using Parameter # 48.
4. When the domestic hot water temperature falls 7.2 degrees below the
desired set temperature for hot water the boiler will begin to heat the
indirect tank. To change this switch-on differential adjust Parameter #36
to the desired value. The switch-off differential can be set separately using
Parameter #37. The default value for this parameter is zero.
Using a field-supplied aquastat:
1. Wire your field-supplied aquastat to the low voltage terminals #9 and #10
on the boiler main control panel.
2. Within the “Boiler Settings” menu set Parameter #35 to “2”.
3. Adjust the field-supplied aquastat to the desired tank temperature
according to the manufacturers instructions .
4. Upon a call for heat from the aquastat the boiler will target a supply
temperature of DHW Set point + DHW Extra. The burner will cycle on/off
based upon a +/- 3.6 degree differential of the target supply temperature of
176 °F.
Depending upon which DHW Mode is selected (Mode 1 = 10 K ohm sensor or Mode
2 = Aquastat) will then determine which of the following parameters can be used to
adjust the hot water operation.
DHW Parameter DHW Mode Description Default Value Range
35 - DHW Mode 0 0 - 2
36 1 DHW Tank Hyst. Down 7.2 0 – 36 °F
37 1 DHW Tank Hyst. Up 0 0 – 36 °F
38 1 DHW Supply Extra 54 0 – 54 °F
42 1 & 2 DHW Priority 0 0 - 2
43 1 & 2 DHW Max Priority Time 30 1 – 255 min.
44 1 & 2 DHW Pump Overrun 15 0 – 255 sec.
48 1 DHW/Tank Setpoint 120 104 – 140 °F
Table 12

18 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
03.2018 |Bosch Thermotechnology Corp.
Data subject to change
7 Cascade Operation
7.1 Cascade operation settings
Parameter Description
Permit Emergency Mode
(parameter #72)
Enable Emergency Mode in a multiple boiler cascade installation to ensure that any dependent boiler can operate
independently should communication with the lead boiler be interrupted or the lead boiler loses communication with
the supply sensor. The dependent boiler will operate at a predetermined “emergency” set point which is set using
Parameter #74. Default setting for this parameter is “Disabled”.
Boiler Address
(parameter #73)
Boiler Address must be changed when setting up a multiple boiler cascade installation. The default address of every
boiler is set to “0”. In a cascade application, the Managing or lead boiler must be set to Address = 1. All other boilers
within the cascade must be set to the next address value. Default setting for Boiler Address is “0”. Adjustable from
0 to 16.
Emergency Setpoint
(parameter #74)
"Emergency Setpoint is the fixed set point which a boiler will operate at within a cascade installation if that boiler has
lost communication with the Managing or lead boiler or the lead boiler loses communication with the supply sensor.
Parameter #72 must be “Enabled” on each dependent boiler and Emergency Set point set for the desired Emergency
temperature at which the boiler is to operate at should the boiler lose communication with the Managing boiler or the
lead boiler loses communication with the supply sensor. Default setting is 113° F. Adjustable from 68 °F to 149 °F.
Delay Period Start Next Boiler
(parameter #75)
The amount of time in seconds which must pass once the previous boiler in the cascade rotation is above the power
percentage defined in parameter #82 (next boiler start rate) and the system supply sensor is below the target
temperature by the value defined in parameter #77 – Differential Down Start Boiler. Default value is 15 seconds.
Adjustable from 5 to 300 seconds.
Delay Period Stop Next Boiler
(parameter #76)
The Amount of time in seconds which must pass once the last boiler turned on in the rotation has dropped below the
power percentage defined in parameter #83 (next boiler stop rate). Default value is 15 seconds. Adjustable from 5
to 300 seconds.
Differential Down Start Boiler
(parameter #77)
In a cascade installation the first or next boiler will be enabled when the system supply sensor is less than the target
system set point minus the value of “Differential Down Start Boiler” for a period of time equal to parameter #75
(delay period start next boiler).
Differential Up Stop Boiler
(parameter #78)
If the temperature of the system supply sensor exceeds a temperature greater than System Target Temperature +
Differential UP all boilers in the cascade will be stopped.
"Max. Setpoint Offset Down
(parameter #79)"
In order to achieve the desired Target System Supply Temperature during a call for heat the boilers may need to
operate at temperatures greater than or less than the desired Target System Supply Temperature. The operating
range in which the boilers are allowed to adjust the individual boiler supply temperatures is defined by the
Offset Down and Offset Up (parameter #80) values. Each dependent boiler will display a “Calculated Setpoint”
temperature on the display which will be within this Offset Range either above or below the overall Target System
Supply Temperature. Default value of Offset UP is 18 F. Adjustable from 0 F to 36 F.
Table 13

Control Operations Guide Bosch Buderus SSB255 | SSB399 | SSB512 Boilers | 19
Bosch Thermotechnology Corp. |03.2018 Data subject to change
Parameter Description
Max. Setpoint Offset UP.
(parameter #80)
See Parameter #79 for explanation of Offset UP and Offset Down. Default value of Offset UP is 18 °F. Adjustable
from 0 °F to 36 °F.
Start Modulation Delay Factor
(parameter #81)
The Managing boiler will calculate the difference between the System Target Setpoint and the measured System
Supply Temperature once a period of time equal to Delay Period Start Next Boiler x Start Modulation Delay Factor has
passed. Default value for Modulation delay is 5. Adjustable from 0 to 60.
Next Boiler Start Rate
(parameter #82)
"The percentage of burner power a boiler must reach before the Managing boiler will begin the process of bringing on
the next boiler within the cascade. See Parameter
#75 for further information on the amount of time which must pass at this power percentage before the next boiler in
the cascade rotation is enabled. Default value is 80%. Adjustable from 10% to 100%."
Next Boiler Start Rate
(parameter #83)
The percentage of burner power a boiler must reach before the Managing boiler will begin the process of turning
off the last boiler enabled within the cascade rotation sequence. See Parameter #76 for further information on
the amount of time which must pass at this power percentage before a boiler is turned off. Default value is 30%.
Adjustable from 10% to 100%.
Boiler Rotation Interval
(parameter #84)
The amount of time (in Days) which will define the boiler rotation interval. Default value is 1 day. Adjustable from 0
(disable rotation) to 30 days.
Domestic Hot Water Boiler Assign
(parameter #85) Not available
Table 14

20 |Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
03.2018 |Bosch Thermotechnology Corp.
Data subject to change
7.2 Cascade operation - set-up of boilers
1. Connect up to 16 boilers together using standard 18/2 thermostat cable.
The Cascade connections can be found on the low voltage terminal block at
contacts #1 and #2.
These connections are polarity sensitive.
Figure 7
123
CASCADE
LINK
123
CASCADE
LINK
Boiler 1
Boiler 2 Boiler 16
...
123456789
10 11 12 13 14
CASCADE
LINK
MOD
BUS
Gas
Switch
Out
Door
DHW Tank
Sensor
Room
Thermostat
Supply
Sensor
2. Determine which boiler in the cascade will be the “Managing” boiler. All
system sensors (i.e. Outdoor air sensor, System Supply Temperature
sensor, DHW Sensor) should be wired to the “Managing boiler”
3. The “S4” switch on the control board of the managing boiler must be in
the “ON” position which means the switch should be in the “Up” position
– default position from the factory is “ON”. The “S4” switch is located on a
small cut-out on the front of the main control board of the boiler. All other
boilers in the cascade should have the S4 switch in the “Off” or “Down”
position.
WARNING:
Never adjust the S4 switch with the power on – always turn
power off first before changing the S4 switch position.
Figure 8
ON
OFF
S4
4. Set the address of each boiler in the Cascade. The Managing boiler
should be set for Address #1. All other boilers in the cascade should be set
for an address of 2 thru 16. To Access the address setting of each boiler:
Press “Menu”
Use down Arrow on the keypad and highlight “Settings” then push
the “OK” button
Highlight “Boiler Settings” then push the “OK” button
If requested, enter the installer setting password of “0300” using
the keypad then press “OK”
Scroll to Parameter # 73 “Boiler Address”. Once highlighted, use
the Right Arrow button to highlight the default value of “0” and use
the “Up” or “Down” Arrow to set the correct address of the boiler.
Press “OK” button to confirm and set the new address value.
Repeat the steps above for each boiler in the cascade being sure
not to set the same address for any two boilers in the cascade.