Strebel S-CB Px 120 User manual

STREBEL
S-CB PX 120 Boiler
Wall Hung High Efficiency Condensing Boiler
Installation, Operating & Maintenance Manual
Please read and understand before commencing installation and leave the manual with the customer for future reference.
2017-05-01 v1

3
TABLE OF CONTENTS
INTRODUCTION………………………………………………………………………………………………….....5
Strebel Ltd is not accountable for any damage caused by incorrect following the mounting instructions.6
For service and repair purposes use only original Strebel spare parts. ....................................................6
1. SAFETY GUIDELINES ................................................................................................................................6
2. TECHNICAL DATA OF THE STREBEL S-CB PX 120...............................................................................7
2.1. FUNCTIONAL INTRODUCTION............................................................................................................. 7
2.2. TECHNICAL SPECIFICATIONS DATASHEET........................................................................................... 8
2.3. ERP SPECIFICATIONS DATASHEET.................................................................................................. 10
3. DIMENSIONS.............................................................................................................................................11
4. ACCESSORIES AND UNPACKING..........................................................................................................12
4.1. ACCESSORIES............................................................................................................................... 12
4.2. UNPACKING................................................................................................................................... 12
5. INSTALLATION OF THE STREBEL S-CB PX 120 ..................................................................................13
5.1. GENERAL NOTES ........................................................................................................................... 13
5.2. MOUNTING THE BOILER.................................................................................................................. 14
6. CONNECTIONS WATER SIDE. ................................................................................................................15
6.1. BOILER CONNECTIONS ................................................................................................................... 15
6.1.1. Mounting ........................................................................................................................... 15
6.1.2. Gas connection................................................................................................................. 15
6.2. CONDENSATE DRAIN CONNECTION.................................................................................................. 16
6.3. FLOW AND RETURN CONNECTIONS.................................................................................................. 16
6.4. THE EXPANSION VESSEL................................................................................................................. 17
6.5. PRESSURE RELIEF VALVE............................................................................................................... 17
6.6. BYPASS ........................................................................................................................................ 17
6.7. PUMP FUNCTIONALITY.................................................................................................................... 17
6.8. FROST PROTECTION ...................................................................................................................... 17
6.9. INSTALLING A STRAINER AND/OR DIRT SEPARATOR........................................................................... 18
6.10. WATER QUALITY ............................................................................................................................ 18
6.11. PLASTIC PIPING IN THE HEATING SYSTEM......................................................................................... 19
6.12. AUTOMATIC AIR VENT..................................................................................................................... 19
6.13. AUTOMATIC WATER FILLING SYSTEMS ............................................................................................. 19
6.14. WATER PRESSURE......................................................................................................................... 20
6.15. CHEMICAL WATER TREATMENT ....................................................................................................... 20
6.16. UNDER FLOOR HEATING ................................................................................................................. 20
6.17. FLUSH THE SYSTEM WITH FRESH WATER......................................................................................... 20
6.18. INSTALLATION EXAMPLES ............................................................................................................... 21
6.18.1. Example of a normal single boiler heating circuit (preferable).......................................... 21
6.18.2. Example of a multiple boiler heating circuit ...................................................................... 21
7. HYDRAULIC GRAPH BOILER RESISTANCE (mWC).............................................................................22
7.1. HIGH EFFICIENCY PUMP.................................................................................................................. 22
7.2. PUMPS:ELECTRICAL POWER LIMITS............................................................................................... 23
7.3. PUMP INSTALLATION...................................................................................................................... 23
8. FLUE GAS DISCHARGE AND AIR SUPPLY SYSTEM...........................................................................24
8.1. GENERAL...................................................................................................................................... 24
8.2. C63 CERTIFIED.............................................................................................................................. 24
8.3. FLUE TERMINAL............................................................................................................................. 25
8.3.1. Horizontal Flue Terminal Positioning................................................................................ 25
8.3.2. Vertical Flue Terminal Positioning .................................................................................... 25
8.3.3. Common Flue / Ducts ....................................................................................................... 25
8.4. AIR SUPPLY................................................................................................................................... 25
8.4.1. Combustion air quality ...................................................................................................... 25
8.4.2. Air supply through humid areas........................................................................................ 25
8.5. PIPE HEIGHTS ON A FLAT ROOF....................................................................................................... 26
8.6. FLUE GAS OUTLET &COMBUSTION AIR INLET CALCULATION EXAMPLES.............................................. 27
8.7. SIX TYPICAL EXAMPLES.................................................................................................................. 28
8.7.1. Example A: Twin pipe system (C63)................................................................................. 28

4
8.7.2. Example B: Twin pipe system with concentric roof terminal (C33)...................................28
8.7.3. Example C: Single flue gas outlet. Air supply from boiler room........................................30
8.7.4. Example D: Concentric flue gas/air supply pipe (roof-mounted).......................................31
8.7.5. Example E: Concentric system Wall outlet C13(wall-mounted)........................................31
8.7.6. Example F: Separate air supply duct & flue duct in different pressure zone (C53) ..........33
9. ELECTRICAL INSTALLATION.................................................................................................................34
9.1. GENERAL.......................................................................................................................................34
9.2. ELECTRICAL CONNECTIONS ............................................................................................................34
9.3. FUNCTIONS OF THE CONNECTIONS..................................................................................................34
9.4. ELECTRICAL SCHEMATICS...............................................................................................................36
9.5. SENSOR VALUES AND CONVERSION TABLES.....................................................................................38
10. USER INTERFACE ...................................................................................................................................39
10.1. CONTROL PANEL /DISPLAY UNIT......................................................................................................39
10.2. CONTROL PANEL MENU STRUCTURE................................................................................................40
10.3. DISPLAY DURING OPERATION..........................................................................................................42
10.4. MONITOR SCREENS........................................................................................................................43
10.5. SERVICE FUNCTION........................................................................................................................45
10.6. SCHORNSTEINFEGER FUNCTION......................................................................................................46
10.7. PROGRAMMING IN STANDBY MODE ..................................................................................................47
10.8. SETTING THE TIME &DATE..............................................................................................................47
10.9. SET POINTS ...................................................................................................................................48
10.10. SETTING THE TIMER PROGRAMS......................................................................................................49
10.11. SETTING THE OUTDOOR SPECIFICATIONS.........................................................................................52
10.12. CHECKING THE OPERATING HISTORY...............................................................................................56
10.13. CHECKING THE FAULT HISTORY.......................................................................................................57
10.14. SETTING THE MAINTENANCE SPECIFICATIONS...................................................................................58
10.15. SETTING THE USER LOCK................................................................................................................61
10.16. SETTING THE PARAMETERS WITH THE DISPLAY MENU .......................................................................62
10.17. FAULT CODES DISPLAY ...................................................................................................................69
10.17.1. Lock-out codes..................................................................................................................69
10.17.2. Blocking codes ..................................................................................................................70
10.17.3. Maintenance attention messages......................................................................................71
11. CONTROLLING OPTIONS AND SETTINGS ...........................................................................................72
11.1. GENERAL.......................................................................................................................................72
11.1.1. Extra boiler control.............................................................................................................72
11.1.2. Max cooling time................................................................................................................72
11.1.3. Temperature display on/off................................................................................................72
11.1.4. Water pressure..................................................................................................................72
11.1.5. Gas type selection.............................................................................................................72
11.1.6. Soft start option .................................................................................................................73
11.1.7. Pump mode (EC technology) ............................................................................................73
HEATING ....................................................................................................................................................74
11.1.8. Controlling behaviour settings...........................................................................................74
11.1.9. Room thermostat on/off.....................................................................................................75
11.1.10. Room thermostat OPEN THERM......................................................................................75
11.1.11. Outdoor temperature related flow control..........................................................................75
11.1.12. 0-10 Vdc Remote flow temperature set point....................................................................75
11.1.13. 0-10 Vdc Remote burner input control ..............................................................................76
11.1.14. Timer contact function.......................................................................................................76
11.2. INDIRECT HOT WATER /CALORIFIER.................................................................................................77
11.2.1. Pump and 3-way valve control ..........................................................................................77
11.2.2. Tank thermostat.................................................................................................................77
11.2.3. Tank sensor.......................................................................................................................77
11.2.4. Low/high flow temperature to tank coil..............................................................................78
11.2.5. Heating and hot water switching time................................................................................79
11.2.6. Heating and hot water switching at sudden temperature drop..........................................79
11.2.7. Anti-Legionnaires’ disease function (pasteurisation).........................................................80
11.3. CASCADE CONTROL........................................................................................................................81
11.3.1. Parameter settings for cascaded boilers...........................................................................81
11.3.2. Monitor screens.................................................................................................................83
11.3.3. Output control and boiler sequence ..................................................................................83

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12. COMMISSIONING THE BOILER...............................................................................................................84
12.1. FIRST:FLUSHING THE BOILER WITH WATER...................................................................................... 84
12.2. SECOND:FILLING &VENTING THE BOILER AND THE SYSTEM.............................................................. 84
12.3. THIRD:CHECK THE WATER FLOW .................................................................................................... 84
13. STARTING THE BOILER ..........................................................................................................................86
13.1. GENERAL...................................................................................................................................... 86
13.2. FIRING FOR THE FIRST TIME............................................................................................................ 86
14. ADJUSTING AND SETTING THE BURNER ............................................................................................87
14.1. INTRODUCTION.............................................................................................................................. 87
14.1.1. Adjustment tables ............................................................................................................. 87
14.1.2. Adjustment values............................................................................................................. 88
14.1.3. Setting screws gas valve: drawing.................................................................................... 89
14.1.4. Adjustment actions: general scheme................................................................................ 90
14.2. ADJUSTING IN CASE OF A NEW BOILER,OR AFTER MAINTENANCE (CASE A)........................................ 91
14.2.1. General remark................................................................................................................. 91
14.2.2. Checking and adjusting at maximum load........................................................................ 91
14.2.3. Checking and adjusting at minimum load......................................................................... 91
14.3. ADJUSTING IN CASE OF VALVE REPLACEMENT OR GAS CONVERSION (CASE B)................................... 91
14.3.1. General remarks ............................................................................................................... 91
14.3.2. Checking and adjusting at maximum load........................................................................ 91
14.3.3. Checking and adjusting at minimum load......................................................................... 91
14.4. ADJUSTING PROCEDURES .............................................................................................................. 91
14.5. GAS CONVERSION PROPANE OR B/P............................................................................................... 93
15. PUTTING THE BOILER OUT OF OPERATION........................................................................................95
15.1. OUT OF OPERATION:ON/OFF FUNCTION .......................................................................................... 95
15.2. OUT OF OPERATION:POWER OFF.................................................................................................... 95
16. FAULT CODES AND BLOCKING CODES...............................................................................................96
16.1. FAULT CODES................................................................................................................................ 96
16.2. BLOCKING CODES........................................................................................................................ 101
16.3. MAINTENANCE REMINDER FUNCTION............................................................................................. 105
17. MAINTENANCE.......................................................................................................................................106
17.1. GENERAL.................................................................................................................................... 106
17.2. ANNUAL INSPECTION &MAINTENANCE........................................................................................... 106
18. USER INSTRUCTIONS ...........................................................................................................................109
INSTALLATION EXAMPLES.........................................................................................................................110
19. Strebel S-CB PX 120...............................................................................................................................114
19.1. SPARE PARTS EXPLODED VIEW AND PART NUMBERS ...................................................................... 114

6
INTRODUCTION
This manual is written for:
▪The Installer.
▪The System Design Engineer.
▪The Service Engineer.
▪The User.
The following symbol is used in this manual:
Warning: Important information concerning the safety of persons and/or the appliance.
Strebel Ltd is not accountable for any damage caused by incorrect following the mounting instructions.
For service and repair purposes use only original Strebel spare parts.
All documentation produced by the manufacturer is subject to copyright law.
1. SAFETY GUIDELINES
Carefully read all the instructions before commencing installation.
Keep these instructions near the boiler for quick reference.
The appliance should be installed by a skilled installer such as GAS SAFE registered person, electrical work carried
out by a qualified person, all according to national and regional standards.
Failure to comply with these regulations could deem the warranty invalid. This appliance must be installed in
accordance with the rules that apply and only be used in an adequately ventilated space conforming to standards
in place.
Without written approval of the manufacturer the internals of the boiler may not be changed. When changes are
executed without approval, the boiler certification becomes invalid.
Commissioning, maintenance and repair must be done by a skilled installer/engineer, according to all applicable
standards and regulations.
What to do if you smell gas:
▪Don't use any electrical equipment.
▪Don't press any switches.
▪Close the gas supply.
▪Ventilate the room (open the windows and/or outside boiler room doors).
▪Immediately warn the installer.
The manufacturer / supplier is not liable for any damage caused by inaccurately following these mount-
ing instructions. Only original parts may be used when carrying out any repair or service work.
This appliance is not intended for use by persons (including children) with reduced physical, sensory
or mental capabilities, or lack of experience and knowledge, unless they have been given supervision
or instruction concerning use of the appliance by a person responsible for their safety. Children should
be supervised to ensure that they do not play with the appliance.

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2. TECHNICAL DATA OF THE STREBEL S-CB PX 120
2.1. Functional introduction
The S-CB PX 120 boilers are central heating boilers with a maximum high efficiency. Such a performance can be
reached by, amongst other things, using a special heat exchanger made of stainless steel. The heat exchanger
allows the flue gases to cool down below the condensation point, releasing extra heat. This immediately improves
the efficiency considerably.
The S-CB PX 120 boiler is standard set for Natural Gas G20
Gases used must meet the European standard EN 437.
Fuel used should have sulphur rates according to the European standard, a maximum annual peak over a short
period of time of 150 mg/m3and an annual average of 30 mg/m3.
Boiler control includes:
▪Cascade control for up to twelve boilers.
▪Remote operation and heat demand indication from each boiler.
▪Weather compensation control.
▪Calorifier control.
Connections for:
▪Boiler pump.
▪0-10 VDC remote flow temperature (set point) control.
▪0-10 VDC remote burner input control.
▪Outdoor temperature sensor.
▪External calorifier pump or diverter valve.
Cascade control
When using the integrated cascade control, a maximum of twelve boilers can be controlled in a cascade configu-
ration. By the use of an appropriate external control, this number may be increased at will.
0-10 VDC connection available
The boiler flow temperature or power input can be controlled by an external 0-10 VDC signal. When a number of
boilers are cascaded, the signal should be directed to the master boiler only. A signal of 1,48 Volt will switch on
the boiler(s), less than 1,4 Volt will switch off the boiler(s).
Time program
For both central heating and hot water function of the boiler, time programs with three programmable periods per
day are available. These time programs are set and activated by entering the desired settings directly at the boiler
control panel.

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2.2. Technical specifications datasheet
GENERAL
Product Identification Number
-
CE 0063 BP3254
Classification
-
UK II2H3B/P
Gas Appliance Type
-
B23, B23P; C13, C33, C43, C53, C63, C83
Type boiler
-
Strebel S-CB PX 120
Water content est.
Litre
8,3
Weight (empty)
kg
78
Dimensions (h x w x d)
mm
842 x 476 x 486
Flow/return connection (boiler)
inch
R 1"
Gas connection
inch
R ¾"
Parallel connection
mm
Ø 100-100
CENTRAL HEATING [EN437] Values min-max:
Nominal input (Net)
kW
26,0 - 111
Nominal input (Hs) (G20 G25)
kW
28,9 - 123
Nominal input (Hs) (G31) 1
kW
28,3 - 121
Nominal input (Hs) (G30) 1
kW
34,7 - 120
Nom. output 80/60
kW
24,7 - 106
Nom. output 50/30
kW
27,2 - 116
Nom. output 37/30
kW
28,1 - 120
Efficiency 40/30ºC DIN 4702-8
%
up to 110,6 %
GAS CONSUMPTION [EN437] Values min-max:
Natural gas G25.3
m³st/h
3,13 - 13,7
Natural gas G20
m³st/h
2,75 - 11,8
Propane gas G31 1
m³st/h
1,06 - 4,54
Butane/Propane (B/P) G30/G31 1
m³st/h
0,99 - 3,44
Supply pressure nom. 2
G25.3
mbar
25
G20
mbar
20
G31 1
mbar
30/37
G30/G31 1
mbar
50
NOTES
1When using propane or butane, a special air restrictor kit is needed. See accessories list on page
12 and instruction at page 95.
2Below a table is given in which the min. and max. gas supply pressures are mentioned according
to EN437
p nominal [mbar]
p min [mbar]
p max [mbar]
G25.3
25
20
30
G20
20
17
25
G31
30
25
35
37
25
45
G30/G31
50
43
57

9
EMISSION [EN437]
Nominal values at min-max load:
CO2flue gas 3
G20/G25.3
%
8,7 -9,0
G31 1
%
9,3 - 10,3
G30/G31 B/P)1
%
9,3 - 10,4
NOx class [ EN15502-1]
-
6
Flue gas temperature at combustion air
temperature = 20°C
°C
≈ 85-95
Mass flow flue gas [min-max]
Qfluegas condensing
g/s
11,6 - 57,7
Available pressure for the flue system 4
Pa
160
INSTALLATION
Max. flow temperature
°C
90
Available pressure for the
installation at
T = 20 K
mWC
1,8
T = 25 K
mWC
2,4
Pressure CH-system min./max. 5
bar
1-4
ELECTRIC
Power supply
V / Hz
230 / 50
Power consumption
W
150
Protection class
-
IPX4D
NOTES
3CO2of the unit measured/set without the boiler front panel in place
4 Maximum allowed combined resistance of flue gas and air supply piping at high fire
5 When the built-in water pressure sensor is replaced by a water pressure switch, water pressure
may go up to 6,0 bar

10
2.3. ERP specifications datasheet
Technical parameters according the European ERP (Energy Related Products) legislation:
Type Boiler:
S-CB PX 120
Condensing boiler:
Yes
low temperature boiler:
Yes
B11 boiler:
No
Cogeneration space heater:
No
Combination heater:
No
Unit:
Value
Rated heat output
kW
107,7
P-rated (P4) at 60-80⁰C
kW
107,7
Heat output (p1) 30% at 30-37⁰C
kW
36,0
Seasonal space heating energy efficiency (ɳs).
%
92,7
energy efficiency (ɳ4) at 60-80⁰C
%
87,4
energy efficiency (ɳ1) at 30-37⁰C
%
97,5
Auxiliary electricity consumption
At full load (elmax).
kW
0,152
At part load (elmin)
kW
0,027
In standby mode (Psb)
kW
0,004
Other
Standby heat loss (Pstby)
kW
0,076
Ignition burner power consumption (Pign)
kW
0,000
Emissions (Nox) of nitrogen oxides (EN15502-
1:2012+A1:2015)
mg/kWh
45
Sound power level, indoors (EN 15036-1:2006)
dB
63

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3. DIMENSIONS
Combustion air inlet connection
(hole with sealing ring and pipe support bracket)
Flue gas outlet
Condensate discharge.
Flexible hose Ø25/21 x 800 mm
Gas supply connection
Circulation flow connection
Circulation return connection
(Circulation pump side)
461
237
118
311
91
Ø
10
0
495
468
842
65
R 1" (2x) R ¾"
65
76
119
72 235 77
Ø100
176 828 135

12
4. ACCESSORIES AND UNPACKING
4.1. Accessories
Depending on the selected controlling behaviour for the central heating system and/or the optional use of a
calorifier, the following items can be supplied with the boiler. Ask your supplier for the specifications.
Item
Part no.
Outdoor (air) temperature sensor: 12kOhm@25°C (Connect to the boiler connectors).
E04.016.585
External flow temperature sensor for system side of the low loss header: 10kOhm@25°C (to
be mounted to the boiler connections).
E04.016.304
Calorifier temperature sensor: 10kOhm@25°C (Connect to the boiler connectors)
E400277
Flue Conversion Kit from Twin Pipe to Concentric (100-100 100/150)
E400132
Software + interface cable for programming the boiler with a computer (laptop)
E400278
LPG Conversion Kit
E400131
Pump UPML 25-105-130 PWM
(Main cable, signal cable with cable gland, and pump gaskets included)
E400157
4.2. Unpacking
The Strebel S-CB PX 120 boiler will be supplied with the following documents and accessories:
•One “Unpacking instructions” document.
•One “Mounting, user and service instructions” manual.
•One suspension bracket.
•Siphon with condensate discharge hose.
•One spare fuse and two burner door spare nuts, attached to the front of the gas valve.
After delivery, always check the boiler package to see if it is complete and without any defects. Report any
imperfections immediately to your supplier.

13
5. INSTALLATION OF THE STREBEL S-CB PX 120
5.1. General notes
At both sides of the boiler at least 50 mm of clearance should be applied to walls or wall units, 350 mm above the
top side of the boiler and enough distance from the bottom side of the boiler, so that the pump can be mounted
here.
The installation area/room must have the following provisions:
•230 V - 50 Hz power source socket with earth connection.
•Open connection to the sewer system for draining condensing water.
•A sound-deadening wall.
•The wall used for mounting the boiler must be able to hold the weight of the boiler.
Other considerations related to the boiler location.
•The ventilation of the boiler room must meet all applicable standards and regulations, regardless of the se-
lected supply of fresh air to the boiler location.
•Both the air supply and the flue gas tubes must be connected to the outside wall and/or the outside roof.
•The installation area must be dry and frost-free.
•The boiler has a built-in fan that will generate noise, depending on the total heat demand. The boiler location
should minimise any disturbance this might cause. Preferably mount the boiler on a brick wall.
•There must be sufficient lighting available in the boiler room to work safely on the boiler.
•When a boiler is positioned at the highest point of the installation, the supply and return pipes must first protrude
0.5 m above the top of the boiler, before these pipes go to the installation side. In other words, the water level
must always be 0.5 meter above the top of the boiler and an automatic air vent must be installed in the supply
or return pipe. A low-water level protection should also be installed at the installation side.
•Notice the positioning of electrical components in relation to the temperature sensitivity.
•Make sure there is an open connection with the sewer to drain the condensate. This connection should be
lower than the condensate drain level of the boiler:
The boiler must be positioned and installed by a skilled installer in accordance with all applicable standards and
regulations. Commissioning the boiler must be done by a skilled service/commissioning engineer, who is trained
for this type of boiler.

14
5.2. Mounting the boiler
Before mounting and installing the boiler the following connections should be considered:
•Flue gas system and the flue gas pipe connections
•Air supply system and connections
•Flow and return pipe connection and pump position
•Condensate and pressure relief valve drainage
•Power supply (preferably the power connection positioned above the boiler)
All lines/piping must be mounted free of tension. The weight of all the installation components should
be supported separately from the boiler so there will be no standing force on the connections.
Pay attention to this while choosing the mounting position of the boiler.
Determine the position of the flow and return pipes by using the included suspension bracket or a suspension
frame (when supplied).
While marking the holes, ensure that the suspension bracket or frame is perpendicular and the boiler does not lean
forward. If necessary, adjust the position with the adjusting bolts at the lower rear side of the back panel (see draw-
ing).
When the adjusting bolts aren’t sufficient, fill the gap behind the bolts to get the boiler in position. The exact boiler
position lies between the boiler hanging level and hanging slightly backwards. The boiler should not lean forward
in the mounted position.
3. Lock boiler with locking plate
and two bolts
2. Suspend boiler with suspension
bracket on mounting bracket
4. Level boiler using
adjusting bolts
1. Attach mounting bracket to wall
with inclined side facing upwards
Boiler suspension
Detail boiler suspension

15
6. CONNECTIONS WATER SIDE.
6.1. Boiler connections
1 - Return CH
2 - Flow CH
3 - Siphon cleaning point
4 - Condensate drain
5 - Gas
6.1.1. MOUNTING
When mounting the connections, always
make sure that no extra tension, forces
and/or torques are applied to the connecting
pipes and/or the boiler and the boiler sus-
pension. Keep the connections fixed in
place, as shown in the picture, by using two
wrenches.
6.1.2. GAS CONNECTION
Always install a manual shutter valve in the gas supply line, directly underneath the boiler.
NOTICE: This valve is NOT delivered with the boiler.
2
15
4
3

16
6.2. Condensate drain connection
The condensate drain has a 19mm flexible discharge hose. The siphon must
always be filled with water. As a safety measure, the siphon has been provided
with a floating ball, which closes the outlet in case of water absence, preventing
large flue gas leakage.
Use only condensate resistant materials for the external condensate drainage
system. Blockage of this drain might damage the boiler. The drain connection is
correct when the condensate can be seen flowing away, e.g. using a funnel. Any
damage that might occur, when the drain is not installed correctly, is not covered
by the warranty.
There should be an open connection of the condensate hose into the sewage
system. Pressure fluctuations in the sewer system may not affect the pressure
in the condensate drain hose, supplied with the siphon:
The siphon must be checked at least once a year. Disassemble the siphon and clean every part of it.
Check the functioning of the siphon by filling it with water. Then blow into the top condensate inlet, gently
increase the pressure. At some point water starts coming out of the siphon outlet. During this the floating
ball should gradually drop into its seat. By doing this, the ball closing the outlet (almost) completely.
When mounting the siphon, before commissioning the boiler and/or after maintenance, the siphon must
ALWAYS be completely filled with water.
This is a safety measure: the water in the siphon keeps the flue gases from leaking out of the heat
exchanger via the condensate drain.
6.3. Flow and return connections
In the picture, an example is shown of the installation of
the flow and return connections in combination with
several functional and/or safety components. The picture
does not necessarily contain ALL safety components that
may or must be applied - always have the installation
carried out by a skilled installer according to all applicable
standards and regulations.
It is advised to install two service valves underneath the
boiler, so the boiler can be isolated from the heating
system, when needed. The valves must be positioned in
such a way that no safety components like pressure relief
valves and expansion vessels can be isolated from the
boiler.
The boiler pump should always be mounted in the return
pipe of the boiler.
When using a system pump, this pump should always be
mounted in the return pipe of the heating system.
Never use chlorine-based fluxes for soldering any pipes
of the water system.
NOTICE: Accessories in the picture are NOT supplied
with the boiler.
flow return
BOILER
NOT
supplied
with boiler
NOT
supplied
with boiler
boiler bleed
valve for
service
pressure
relief
valve
boiler
service
valves
expansion
vessel
Open connection 
to sewer

17
6.4. The expansion vessel
The capacity of the expansion vessel must be selected and based on the capacity of the central heating system
and the static pressure. Suggested is to fit the expansion vessel in the return pipe of the central heating system. It
can be combined with the drain valve for service.
6.5. Pressure relief valve
The boiler has no internal pressure relief valve. This should be installed in the flow pipe of the heating system and
close to the boiler. When having cascaded boilers, each boiler should have its own pressure relief valve. It is
advised to use a T-piece for this.
Advise is always to install service valves, so the boiler can be isolated from the heating system, when needed.
Make sure that the pressure relief valve is mounted between the boiler and the service valves.
The pressure relief valve must always be installed in such a way that it cannot be isolated from the boiler by a
valve. The specifications and size of the relief valve should be determined by the installer and must comply with
all applicable regulations and boiler capacity.
6.6. Bypass
The boiler has no internal bypass. When many thermostatic valves are being used, the system should have a
bypass to allow an adequate flow when all thermostatic valves are closed. Instead of a bypass also a low-loss
header can be used for this function.
The boiler flow will also be influenced when a pipe of the heating system is frozen/blocked. Make sure all heating
pipes are free from the risk of frost. If there is the risk of freezing of the heating system, all the pipe sections must
be insulated and/or protected with the help of a tracing.
6.7. Pump functionality
High efficiency pump (default settings)
The pump is controlled by a PWM signal from the burner controller. It’s set point is based on a delta T of 20°C.
This means, that when the burner is on full load, delta T = 20°C, and when the burner modulates down, the pump
also modulates down keeping delta T 20°C (provided it is still in range of the lowest limit of the pump).
The delta T monitoring parameters have been set so, that a malfunctioning of the pump or an extreme resistance
in the hydraulic system will be detected by the burner controller. When the limits of these parameters are exceeded,
the display message “dT Block” will be displayed. This message will disappear when the delta T is within limits
again, if not the boiler will go into a lock out after 45 seconds and the display will blink with the message “FlowReturn
dTfault.”Therefore, no commissioning valves should be installed on the primary pipework (boiler side).
ON/OFF pump
If an on/off pump is used, it must be connected to the P3 control (23-24-25).
When this pump has multiple speed settings, make sure it is set at the highest setting and do not change this
setting. The boiler has an internal pump switch that has a programmable delay before it turns off (also for hot
water supply this delay is programmable).
The pump starts running in case of a heat demand. When heat demand stops, the pump will continue to run for a
programmed period and after that it will stop. The pump and (when installed) the three-way valve or hot water
pump for the calorifier can be activated every 24 hours (for a programmable period). This 24-hour cycle starts as
soon as the power supply of the boiler is connected.
6.8. Frost protection
The boiler has a built-in frost protection, that is automatically activating the CH pump when the boiler return tem-
perature drops below the 5°C. When the boiler return temperature drops below the 3°C, the burner is also ignited.
The pump and/or burner will shut down as soon as the return temperature has reached the 10°C. The mentioned
temperatures are related to the temperatures measured by the RETURN sensor of the boiler. This frost protection
function will not fire up the boiler in case of a “general blocking” of the burner demand.
NOTICE: This frost protection is only to reduce the risk of frost damage to the boiler, not the whole system.
•The external pump must be mounted in the return pipe of the boiler.
•The boiler pump must be controlled by the Strebel S-CB PX 120 control. If, for any reason, an
external pump control is applied without written approval of Strebel, the complete warranty on
the S-CB PX 120 and all supplied parts will become invalid.

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Be aware that flow restrictions in the system, caused by frozen pipes, will also prevent the water flow, needed for
the boiler frost protection function to work. Because it concerns a programmable setting, boiler damage caused by
frost/freezing will affect warranty.
6.9. Installing a strainer and/or dirt separator
Always install a strainer (water filter)
and/or a dirt separator on the system
side after a low loss header / Strebel
boiler guard / plate heat exchanger on
the return pipe pipework –not on the
boiler side (primary)! This will ensure
that the water going to the boiler is free
of any flow restrictions. When using a
water filter always check a week after
installation to determine the strainer
cleaning interval. Advice is to mount
valves before and after the strainer,
including an air bleed valve, so the
strainer can be isolated from the heat-
ing circuit for service operations. Clean
water is very important, blocked and/or
polluted heat exchangers, including
failures and/or damages caused by this
blockage are not covered by the
warranty.
6.10. Water quality
The pH value of the water must be within the following limits: 7,5 < pH < 9,5. This pH value is reached with the
steady conditions. These steady conditions will occur, when after filling the heating system (pH around 7) with
fresh water, the water will lose its air because of the air bleeding operation and heating up (dead water conditions).
Water hardness must be within the following limits:
3,5° Clark (50 ppm CaCO3) < total hardness < 10,5° Clark (150 ppm CaCO3)
When the water might contain aluminium particles, this should be of a maximum of 8.5 ppm. If there is any risk of
contamination of the water by any kind of debris/chemicals in the period after installing, a plate heat exchanger
should be used to separate the boiler circuit from the heating circuit (see drawing below).
It is advised to prevent the possible air intake and water leakage of the central heating system. Fresh oxygenated
water might damage the heat exchanger of the boiler and should therefore be prevented. Usual spots where air is
most likely to seep in are: suction gaskets, pumps, air valve working as a venting pipe, O-rings / gaskets in stuffing
box, under floor heating pipes.
SYSTEM WITH DIRT SEPARATOR
SYSTEM WITH STRAINER
SYSTEM WITH STRAINER AND DIRT SEPARATOR
DIRT SEPARATOR
DIRT SE-
PARATOR
WATER RE-
TURN FROM
SYSTEM
WATER RE-
TURN
FROM SYS-
TEM
WATER
RETURN
FROM
SYSTEM
WATER FLOW
TO BOILER(S)
WATER FLOW
TO BOILER(S)
WATER
FLOW TO
BOILER(S)
DIRT
BLEED
VALVE
DIRT
BLEED
VALVE
AIR
BLEED
VALVE
AIR
BLEED
VALVE
VALVE
VALVE
VALVE
VALVE
STRAINER
(WATER FILTER)
STRAINER
(WATER FILTER)

19
6.11. Plastic piping in the heating system
When plastic pipes are used in the central heating system and NOT oxygen diffusion proof to standard DIN 4726,
these should be separated from the boiler system by using a plate heat exchanger. Diffusion (through the plastic)
can cause air to enter the heating system. This could damage the boiler, pumps and other components in the
system. Be aware that plastic piping is often used in under floor heating systems. When no measures have been
taken to prevent the entrance of air into the boiler system, the warranty of the boiler and any boiler part may be
deemed invalid.
6.12. Automatic air vent
This automatic air vent is only used for bleeding the air from the heat exchanger of the boiler, while filling the
system. Externally measures must be taken to bleed air from the heating system, using air separators in combina-
tion with automatic air vents. DE-AERATION PROGRAM. When the unit is fired for the first time the unit starts a
de-aeration program. One cycle means 5 seconds pump running and 5 seconds pump off. A complete de-aeration
program consists out of THREE cycles. The de-aeration program can be interrupted/stopped by briefly pressing
the service button.
6.13. Automatic water filling systems
When using an automatic water refill system some precautions should be taken (fresh water is bringing fresh
oxygen into the system), like installing a water meter to measure and evaluate the total water volume that is added
to the system. Some form of logging should take place, so that continuously filling of the system with large amounts
of oxygen rich fresh water, indicating leakage, is detected in time.
boiler
boiler
boiler
boiler
heating
zone
plate heat
exchanger
plate
heat exchanger
heating
zone

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6.14. Water pressure
First and for all, the installation should be designed and built conform all applicable regulations and standards,
including the right safety valves.
IMPORTANT: Always keep the pressure in the boiler lower than the value at which its safety valve opens.
Sensor
A water pressure sensor has been built into the boiler. With this sensor, the minimum water pressure in the boiler
is 0,8 bar and the maximum pressure is up to 4,0 bar (sensor values). The normal water pressure is supposed to
be between 1,5 and 2,0 bar.
The pressure sensor will stop the boiler from firing when the water pressure drops below 0.8 bar, and start the
boiler firing again when the water pressure reaches above the 1.0 bar. These values can be changed in the boiler
control settings.
Higher pressure systems (e.g. in high buildings)
If pressures higher than 4,0 bar occur in the heating system, the best solution is to separate the system from the
boiler by means of a plate heat exchanger. Now the boiler pressure can still be under 4,0 bar and the boiler control
remains as described above.
Without plate heat exchanger, above 4,0 bar, a water pressure switch has to be built into the boiler instead of the
water pressure sensor - the maximum allowed value in the boiler now is 6,0 bar and the boiler control needs to be
adjusted.
6.15. Chemical water treatment
The chemical compatibility of several products for treatment of the central heating equipment has been tested on
the heat exchangers and the boilers. A list of corrosion inhibitors in preventative and curative treatment for gas
fired central heating boilers can be supplied by the manufacturer.
6.16. Under floor heating
When using an under-floor heating system, the boiler circuit must be separated from the heating circuit with a plate
heat exchanger.
6.17. Flush the system with fresh water
The water of the boiler and heating circuit should be free of any particles, debris and pollution. Therefore, the
complete installation must always be thoroughly flushed with clean water before installing and using the boiler(s).