Viessmann VITOCROSSAL 300 User manual

for use by heating contractor
Please file in Service Binder
5673 649 - 03 06/2015
Service Instructions
VITOCROSSAL 300
Vitocrossal 300
CU3A Series 26 to 57
Floor mounted, gas-fired condensing boiler with MatriX gas burner and Lambda Pro control
For operation with natural gas and liquid propane gas
Heating input 19 to 199 MBH
5.6 to 58 kW
Read and save these instructions
for future reference.
Product may not be exactly as shown
IMPORTANT
H

Safety
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Vitocrossal 300 CU3A 26 to 57 Service
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Safety, Installation and Warranty Requirements
Please ensure that these instructions are read and understood before commencing installation. Failure to comply with
the instructions listed below and details printed in this manual can cause product/property damage, severe personal
injury, and/or loss of life. Ensure all requirements below are understood and fulfilled (including detailed information
found in manual subsections).
WARNING
Installers must follow local regulations with respect to
installation of carbon monoxide detectors. Follow the
Viessmann maintenance schedule of the boiler contained
in this manual.
Product documentation
Read all applicable documentation before commencing
installation. Store documentation near boiler in a
readily accessible location for reference in the future
by service personnel.
For a listing of applicable literature,
please see section entitled “Important
Regulatory and Installation Requirements”.
Warranty
Information contained in this and
related product documentation must
be read and followed. Failure to do
so renders the warranty null and void.
Licensed professional heating contractor
The installation, adjustment, service and maintenance
of this equipment must be performed by a licensed
professional heating contractor.
Please see section entitled
“Important Regulatory and Installation
Requirements”.
Contaminated air
Air contaminated by chemicals can cause by-products
in the combustion process, which are poisonous to
inhabitants and destructive to
Viessmann equipment.
For a listing of chemicals which
cannot be stored in or near the
boiler room, please see subsection
entitled “Mechanical room” in the
“Installation Instructions”.
Advice to owner
Once the installation work is complete, the heating
contractor must familiarize the system operator/
ultimate owner with all equipment, as well as safety
precautions/requirements, shutdown procedure, and
the need for professional service annually before the
heating season begins.
Carbon monoxide
Improper installation, adjustment, service and/or
maintenance can cause flue products to flow into
living space. Flue products contain poisonous carbon
monoxide gas.
For information pertaining to the
proper installation, adjustment, service
and maintenance of this equipment to
avoid formation of carbon monoxide,
please see subsection entitled
“Mechanical room” and “Venting requirements”
in the “Venting System Installation Instructions”.
Fresh air
This equipment requires fresh air for
safe operation and must be installed
ensuring provisions for adequate
combustion and ventilation air exist.
For information pertaining to the
fresh air requirements of this product,
please see subsection entitled
“Mechanical room” in the “Installation
Instructions”.
Equipment venting
Never operate boiler without an installed venting
system. An improper venting system can cause
carbon monoxide poisoning.
For information pertaining to
venting and chimney requirements,
please see section entitled “Venting
Connection”. All products of
combustion must be safely vented
to the outdoors.
Operating and Service Documentation
It is recommended that all product documentation such
as parts lists, operating and service instructions be handed
over to the system user for storage. Documentation is to
be stored near boiler in a readily accessible location for
reference by service personnel.
WARNING
This boiler requires fresh air for safe operation and must
be installed with provisions for adequate combustion
and ventilation air (in accordance with local codes and
regulations of authorities having jurisdiction).
Do not operate this boiler in areas with contaminated
combustion air. High levels of contaminants such as
dust, lint or chemicals can be found at construction
sites, home renovations, in garages, workshops, in dry
cleaning/laundry facilities, near swimming pools and in
manufacturing facilities.
Contaminated combustion air will damage the boiler
and may lead to substantial property damage, severe
personal injury and/or loss of life. Ensure boiler/burner is
inspected and serviced by a qualified heating contractor
at least once a year in accordance with the Service
Instructions of the boiler.

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Vitocrossal 300 CU3A 26 to 57 Service
About these Service Instructions

Take note of all symbols and notations intended to draw attention to potential hazards or important product
information. These include “WARNING”, “CAUTION”, and “IMPORTANT”. See below.
IMPORTANT
Warnings draw your attention to the presence of
potential hazards or important product information.
Cautions draw your attention to the presence of
potential hazards or important product information.
Helpful hints for installation, operation or maintenance
which pertain to the product.
This symbol indicates that additional, pertinent
information is to be found.
This symbol indicates that other instructions must
be referenced.
WARNING
Indicates an imminently hazardous situation which,
if not avoided, could result in loss of life, serious injury
or substantial product/property damage.
CAUTION
Indicates an imminently hazardous situation which,
if not avoided, may result in minor injury or product/
property damage.
Safety, Installation and Warranty Requirements (continued)
WARNING
Inhaling of fiberglass wool and/or ceramic fiber
materials is a possible cancer hazard. These materials
can also cause respiratory, skin and eye irritation.
Fiberglass wool and ceramic fiber materials
WARNING
Appliance materials of construction, products of
combustion and the fuel contain alumina, silica, heavy
metals, carbon monoxide, nitrogen oxides, aldehydes
and/or other toxic or harmful substances which can
cause serious injury or loss of life and which are
known to the State of California to cause cancer,
birth defects and other reproductive harm. Always
use proper safety clothing, respirators and equipment
when servicing or working nearby the appliance.
The state of California has listed the airborne fibers of
these materials as a possible cancer hazard through
inhalation. When handling these materials, special care
must be applied.
First aid measures
- If eye contact occurs, flush eyes with water to remove
dust. If symptoms persist, seek medical attention.
- If skin contact occurs, wash affected areas gently
with soap and warm water after handling.
Suppliers of fiberglass wool products recommend the
following precautions be taken when handling these
materials:
- Avoid breathing fiberglass dust and contact with
skin and eyes.
- Use NIOSH approved dust/mist respirator.
- Wear long-sleeved, loose fitting clothing, gloves
and eye protection.
- Wash work clothes separately from other clothing.
Rinse washer thoroughly.
- Operations such as sawing, blowing, tear-out and
spraying may generate airborne fiber concentration
requiring additional protection.
Suppliers of ceramic fiber products recommend the
following first aid measures:
- Respiratory tract (nose and throat) irritation:
If respiratory tract irritation develops, move the person
to a dust free location.
-Eye irritation: If eyes become irritated, flush immediately
with large amounts of lukewarm water for at least 15
minutes. Eyelids should be held away from the eyeball
to ensure thorough rinsing. Do not rub eyes.
- Skin irritation: If skin becomes irritated, remove soiled
clothing. Do not rub or scratch exposed skin. Wash area
of contact thoroughly with soap and water. Using
a skin cream or lotion after washing may be helpful.
- Gastrointestinal irritation: If gastrointestinal tract
irritation develops, move the person to a dust free
environment.
Safety

Table of Contents
4
Page
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Safety
General Information
Start-up
Service
Safety, Installation and Warranty Requirements..............2
Product documentation..........................................2
Warranty..............................................................2
Licensed professional heating contractor..................2
Contaminated air...................................................2
Advice to owner....................................................2
Operating and Service Documentation......................2
Carbon monoxide...................................................2
Fresh air..............................................................2
Equipment venting.................................................2
Fiberglass wool and ceramic fiber materials..............3
First aid measures..................................................3
About the Service Instructions......................................3
Necessary Tools.........................................................6
Important Regulatory and Installation Requirements........6
Codes..................................................................6
Technical literature................................................6
Initial start-up.......................................................6
Working on the equipment.....................................6
Instructing the system user....................................6
Applicability..............................................................8
Product Information....................................................8
Mechanical Room......................................................9
Filling the Heating System..........................................10
Removing the Front Panels........................................11
Filling Siphon With Water...........................................11
Opening the Control Unit...........................................12
Select Language.......................................................12
Set Time and Date....................................................12
Check Power Supply Connection.................................13
Designating Heating Circuits.......................................13
Setting High Altitude.................................................13
Select Gas Type.......................................................14
Convert Fuel Type to LPG..........................................14
Measuring the Static Pressure and Running Pressure.....15
Set Maximum Output................................................16
Check All Primary and Secondary Circuit
Connections for Leaks...............................................16
Check Gas Pipes and Fittings for Leaks........................16
Perform Combustion Analysis.....................................17
Checking the Direct Vent (coaxial) System Tightness....17
Sequence of Operation and Potential Faults During
Each Startup Cycle....................................................18
Removing the Burner and Checking the Burner Gasket...19
Checking Burner Mesh Assembly and Refractory...........20
Placing the Burner Door in the Service Retainer.............20
Check and Adjust Ignition and Ionization Electrodes......20
Cleaning the Combustion Chamber and Heating Surfaces..21
Separating the Neutralizing System (if installed)................21

Table of Contents
5
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Service (continued)
Coding 1
Coding 2
Diagnosis and Service Scans
Troubleshooting
Function Description
Additional Information
Cleaning and Reconnecting the Condensate Drain System.22
Checking Gaskets and Thermal Insulation Components
on the Boiler.............................................................23
Checking the Diaphragm Expansion Vessel and
System Pressure.......................................................23
Fitting the Burner......................................................24
Clock Natural Gas Meter............................................24
Check CO2Setting...................................................25
Combustion Management System...............................26
Check Functioning Safety Valves................................26
Check Electrical Connections......................................27
Check the Mixing Valve for Obstructions and Leaks......27
Example Layout 1.....................................................28
Example Layout 2.....................................................32
Example Layout 3.....................................................37
Start-up...................................................................42
Menu........................................................……..……42
Functional Description...............................................44
Adjusting the Heating Curves.....................................45
General...................................................................50
Boiler......................................................................51
DHW......................................................................52
Solar......................................................................52
Heating Circuit 1, 2 and 3.........................................53
General ..................................................................57
Boiler......................................................................63
DHW......................................................................64
Solar......................................................................66
Heating Circuit 1, 2 and 3.........................................70
Calling up the Service Level.......................................75
Diagnosis................................................................76
Checking Outputs (relay tests)...................................77
Fault Codes..............................................................78
Corrective Action......................................................86
Internal Extensions EA1............................................91
Control Functions.....................................................93
Wiring Diagram.........................................................94
Fitting the Front Panel...............................................96
Burner Program Sequence of Operation.......................97
Parts Lists....................................................…………98
Installation Fittings.......................……..............……103
Technical Data..........................................…….……104
Maintenance Record................................................106
Lighting and Operating Instructions...........................107

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Necessary Tools
Testing/analysis equipment (Use only calibrated equipment)
HMultimeter to measure 0 - 230V, 0 - 12A AC and
0-100 mA DC
HFlue gas analyzer to measure % CO2or O2(i.e.
Bacharach fluid samplers or suitable electronic analyzer)
HManometer to measure gas pressure 0 to 11 "w.c.
(accurately) and up to 28 "w.c. gas pressure (or a non-
electric Magnehelic® manometer may also be utilized)
HStack thermometer 0 to 500°F (0 to 260°C)
HBacharach calculator or suitable tables to calculate
efficiency
HCarbon monoxide measuring equipment 0 to 400 ppm
Cleaning supplies
HPlastic hand brush
HRags
Special items
HApproved leak detection fluid for natural gas and
liquid propane gas
HPipe joint sealant
General Information
Important Regulatory and Installation Requirements
Codes
The installation of this unit shall be in accordance with
local codes or, in the absence of local codes, use CAN/
CSA-B149.1 or .2 Installation Codes for Gas Burning
Appliances for Canada. For U.S. installations use the
National Fuel Gas Code ANSI Z223.1. Always use latest
editions of codes.
In Canada all electrical wiring is to be done in accordance
with the latest edition of CSA C22.1 Part 1 and/or local
codes. In the U.S. use the National Electrical Code ANSI/
NFPA 70. The heating contractor must also comply with
both the Standard for Controls and Safety Devices for
Automatically Fired Boilers, ANSI/ASME CSD-1, and the
Installation Code for Hydronic Heating Systems, CSA
B214, where required by the authority having jurisdiction.
Technical literature
Literature for the Vitocrossal 300 CU3A boiler:
- Technical Data Manual
- Installation Instructions
- Service Instructions
- Operating Instructions and User’s Information Manual
- Instructions of other Viessmann products utilized and
installed
- Installation codes mentioned in this manual
Leave all literature at the installation site and advise the
system operator/ultimate owner where the literature can
be found. Contact Viessmann for additional copies.
This product comes with several safety instruction labels
attached. Do not remove! Contact Viessmann immediately
if replacement labels are required.
Initial start-up
Initial start-up must be performed by a qualified heating
contractor. Proper completion of the Maintenance
Record by the heating contractor is also required. The
Maintenance Record is located in the Service Instructions.
Working on the equipment
The installation, adjustment, service, and maintenance
of this boiler must be done by a licensed professional
heating contractor who is qualified and experienced in
the installation, service, and maintenance of hot water
boilers. There are no user serviceable parts on the boiler,
burners, or control.
Please carefully read this manual prior to attempting
start-up, maintenance or service. Any warranty is null
and void if these instructions are not followed.
For information regarding other Viessmann System
Technology componentry, please reference
documentation of the respective product.
We offer frequent installation and service seminars to
familiarize our partners with our products. Please inquire.
Ensure main power supply to equipment, the heating
system, and all external controls has been deactivated.
Close main gas supply valve. Take precautions in all
instances to avoid accidental activation of power during
service work.
The completeness and functionality of field supplied
electrical controls and components must be verified by
the heating contractor. These include low water
cut-offs, flow switches (if used), staging controls,
pumps, motorized valves, air vents, thermostats, etc.
Instructing the system user
The installer of the system is responsible to ensure the
system operator/ultimate owner is made familiar with the
system functioning, its activation, and its shut-down.
The following topics must be covered:
- Proper system operation sequence.
- Explain the equipment.
- Demonstrate an emergency shut-down, what to do
and what not.
- Explain that there is no substitute for proper
maintenance to help ensure safe operation.

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Vitocrossal 300 CU3A 26 to 57 Service General Information
Important Regulatory and Installation Requirements (continued)
For installations on the Commonwealth of Massachusetts, the following modifications to NFPA-54 chapter 10 apply:
Excerpt from 248 CMR 5-08:
2(a) For all side-wall horizontally vented gas fueled equipment installed in every dwelling, building or structure used in
whole or in part for residential purposes, including those owned or operated by the Commonwealth and where the side-
wall exhaust vent termination is less than (7) feet above finished grade in the area of the venting, including but not limited
to decks and porches, the following requirements shall be satisfied:
1. INSTALLATION OF CARBON MONOXIDE DETECTORS. At the time of installation of the side-wall horizontal vented gas
fueled equipment, the installing plumber or gas fitter shall observe that a hard wired carbon monoxide detector with an
alarm and battery back-up is installed on the floor level where the gas equipment is to be installed. In addition, the
installing plumber or gas fitter shall observe that a battery operated or hard wired carbon monoxide detector with an
alarm is installed on each additional level of the dwelling, building or structure served by the side-wall horizontal vented
gas fueled equipment. It shall be the responsibility of the property owner to secure the services of qualified licensed
professional for the installation of hard-wired carbon monoxide detectors.
a. In the event that the side-wall horizontally vented gas fueled equipment is installed in a crawl space or an attic, the
hard-wired carbon monoxide detector with alarm and battery back-up may be installed on the next adjacent floor level.
b. In the event that the requirements of this subdivision can not be met at the time of completion of installation, the
owner shall have a period of thirty (30) days to comply with the above requirements; provided, however, that during
said thirty (30) day period, a battery operated carbon monoxide detector with an alarm shall be installed.
2. APPROVED CARBON MONOXIDE DETECTORS. Each carbon monoxide detector as required in accordance with
the above provisions shall comply with NFPA 720 and be ANSI/UL 2034 listed and IAS certified.
3. SIGNAGE. A metal or plastic identification plate shall be permanently mounted to the exterior of the building at a
minimum height of eight (8) feet above grade directly in line with the exhaust vent terminal for the horizontally vented
gas fueled heating appliance or equipment. The sign shall read, in print size no less than one-half (1/2) inch in size,
“GAS VENT DIRECTLY BELOW. KEEP CLEAR OF ALL OBSTRUCTIONS”.
4. INSPECTION. The state or local gas inspector of the side-wall horizontally vented gas fueled equipment shall not
approve the installation unless, upon inspection, the inspector observes carbon monoxide detectors and signage
installed in accordance with the provisions of 248 CMR 5.08(2)(a) 1 through 4.
(b) EXEMPTIONS: The following equipment is exempt from 248 CMR 5.08(2)(a) 1 through 4:
1. The equipment listed in Chapter 10 entitled “Equipment Not Required To Be Vented” in the most current edition
of NFPA 54 as adopted by the Board; and
2. Product Approved side-wall horizontally vented gas fueled equipment installed in a room or structure separate
from the dwelling, building or structure used in whole or in part for residential purposes.
CSD-1 Field Testing of High Limit Switches for Vitocrossal 300 CU3A boilers – where required by law.
VIESSMANN IS NOT RESPONSIBLE FOR ANY DAMAGES THAT THE FOLLOWING TEST PROCEDURE MAY RESULT
IN BY OVERHEATING THE SYSTEM.
The fixed high limit, when tripped, produces a fault that will require manual reset of the boiler control.
Fixed High Limit fault simulation:
- Run the boiler to high fire via relays test.
- Throttle the boiler valve to a point where the burner will run with as little flow as possible.
- When the burner shuts down on the electronic limit, close the ball valve to stop the flow.
- The boiler temperature should continue a steady increase to trip the fixed high limit.
- Once the fixed high limit is tripped, slowly open the boiler valve to safely cool the boiler down.

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Applicability
General Information
When ordering replacement parts, provide the 16-digit
boiler serial number (on the bar code label), located as
shown underneath boiler front enclosure panel. Refer
to page 11 for instructions on how to remove front
enclosure panel.
Model No. CU3A 26
Serial No. 7553000 jjjjjjjjj
Model No. CU3A 35
Serial No. 7553001 jjjjjjjjj
Model No. CU3A 45
Serial No. 7553002 jjjjjjjjj
Model No. CU3A 57
Serial No. 7553003 jjjjjjjjj
Product Information
CAUTION
The boiler serial number must be provided when ordering
replacement parts.
IMPORTANT
Natural gas and liquid propane gas-fired condensing
heating boiler for weather-responsive operation in closed
loop, forced circulation hot water heating systems for
space heating and domestic hot water (DHW) production.
The Vitocrossal 300 CU3A series boiler comes factory
set for operation with natural gas. For a fuel conversion
to liquid propane gas no conversion kit is required.
Boiler model must be selected based on an accurate heat
loss calculation of the building. Ensure boiler model is
compatible with connected radiation.
Vitocrossal 300 CU3A series boilers are factory-tested
and calibrated. Further gas valve adjustments are not
typically required during field start-up.
Follow the Vitocrossal 300 CU3A Venting
System Installation Instructions to vent this
boiler.
Legend
ADigital Vitotronic boiler control unit
BWater-cooled stainless steel combustion chamber
CModulating MatriX gas burner – for extremely clean
combustion
DStainless steel Inox-Crossal heat exchanger
EHighly effective thermal insulation
FFlue gas collector with condensate drain pipe
GCombustion air intake for direct vent (two-pipe)
systems

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Mechanical Room
During the early stages of designing a new home, we recommend that proper consideration be given to constructing a
separate mechanical room dedicated to the gas- or oil-fired heating equipment and domestic hot water storage tank(s).
The boiler must be located in a heated indoor area, near a floor drain, and as close as possible to a wall. Whenever
possible, install the boiler near an outside wall so that it is easy to duct the venting system to the boiler.
Ensure that the boiler location does not interfere with the proper circulation of combustion and ventilation air of other
fuel burning equipment within the mechanical room (if applicable).
The maximum room temperature of the mechanical room where the boiler is located must not exceed 104ºF (40ºC).
HEnsure ambient temperatures are higher than 32°F
(0°C) and lower than 104°F (40°C).
HPrevent the air from becoming contaminated by
halogenated hydrocarbons (e.g. as contained in paint
solvents or cleaning fluids) and excessive dust (e.g.
through grinding or polishing work). Combustion air
for the heating process, and ventilation of the boiler
room must be free of corrosive contaminants. To that
end, any boiler must be installed in an area that has no
chemical exposure. The list to the right indicates the
main, currently known sources.
HAvoid continuously high levels of humidity (e.g. through
frequent drying of laundry).
HNever close existing ventilation openings.
WARNING
If you notice fire coming from the appliance, call the fire
department immediately! Do not attempt to extinguish
the fire unless qualified to do so.
WARNING
Incorrect ambient conditions can lead to damage to
the heating system and put safe operation at risk.
WARNING
Fire causes a risk of burns and explosion!
HShut down the boiler
HClose fuel shut-off valves
HUse a tested fire extinguisher, class ABC.
IMPORTANT
The service life of the boiler’s exposed metallic surfaces,
such as the casing and fan housing, is directly influenced
by proximity to damp and salty marine environments. In
such areas, higher concentration levels of chlorides from
sea spray, coupled with relative humidity, can lead to
degradation of the exposed metallic surfaces mentioned
above. Therefore, it is imperative that boilers installed
in such environments not be installed using direct vent
systems which draw outdoor air for combustion. Such
boilers must be installed using room air dependent vent
systems; i.e. using room air for combustion. The indoor
air will have a much lower relative humidity and, hence,
potential corrosion will be minimized.
Installation area conditions Sources of combustion and ventilation air contaminants
Areas likely to contain contaminants:
HNew building construction
HSwimming pools
HRemodelling areas, hobby rooms
HGarages with workshops
HFurniture refinishing areas
HDry cleaning/laundry areas and establishments
HAuto body shops
HRefrigeration repair shops
HMetal fabrication plants
HPlastic manufacturing plants
HPhoto processing plants
HBeauty salons
Products containing contaminants:
HChlorine-type bleaches, detergents and cleaning
solvents found in household laundry rooms
HPaint and varnish removers
HHydrochloric acid, muriatic acid
HChlorine-based swimming pool chemicals
HSpray cans containing chlorofluorocarbons
HChlorinated waxes and cleaners
HCements and glues
HRefrigerant leaks
HCalcium chloride used for thawing
HSodium chloride used for water softening salt
HPermanent wave solutions
HAdhesives used to fasten building products and other
similar items
HAntistatic fabric softeners used in clothes dryers
Boiler operation in marine environments (damp, salty
coastal areas)

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10
Startup
Filling the Heating System
1. Check the pre-charge pressure of the diaphragm
expansion vessel when the system is still cold.
Note: If the pre-charge pressure of the diaphragm
expansion vessel is lower than the static pressure
of the system, top up with nitrogen until the
precharge pressure 1.5 to 3 psi (0.1 to 0.2 bar)
is higher than the static system pressure.
The static pressure corresponds to the static head.
2. Close the gas shutoff valve.
3. Open any installed shutoff valves.
4. Fill the heating system with water and vent it, until
the fill pressure 1.5 to 3 psi (0.1 to 0.2 bar) is higher
than the pre-charge pressure of the diaphragm
expansion vessel using the boiler drain/fill valve A.
Max. operating pressure: 30 psi (2 bar)
Min. operating pressure: 14 psi (1 bar)
Pressure relief valve: 30 psi (2 bar)
5. Mark the set pressure at temperature and pressure
gauge B.
6. Return the shutoff valves to their operating position.
7. Close boiler drain/fill valve A.
CAUTION
Unsuitable fill water increases the level of deposits and
corrosion, and may lead to damage to the equipment.
HThoroughly flush the entire heating system prior to
filling with water.
HOnly use water of potable quality.
HThe water will have to be softened if it is harder than
8.77 grains / 150 ppm total dissolved solids.
HInhibitors or antifreeze additives suitable for heating
systems may be added manually.

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Vitocrossal 300 CU3A 26 to 57 Service Startup
Removing the Front Panel
Filling Siphon with Water
1. Undo fitting Aof siphon B, remove the siphon and
fill it with water.
Note: There is a risk of flue gas escaping if the
siphon is not filled with water.
2. Refit siphon B.
1. Remove the retaining screw and set aside.
2. Pull the top of the boiler cover away from the boiler,
lift off and set aside.

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Startup
Vitotronic 200, type KW6B
Legend
ATop part of control unit with programming unit
BPushbutton for changing the angle
COn/off switch
Opening the Control Unit
1. Lift the programming unit Ainto the upright position
(the angle of the programming unit can be adjusted
using the pushbutton on the side B).
2. Open the control cover and turn the boiler on by
switching the on/off switch C.
Select the Language
Note: At the commissioning stage, the display is in
American English (EUS) (default setting)
Extended menu:
1.
2. “Settings”
3. “Language”
4. Set the required language with .
Setting the time and date (if required)
During commissioning, or after prolonged time out of use,
the time and date need to be reset.
Extended menu:
1.
2. “Settings”
3. “Time / Date”
4. Set current time and date.
Set the Time and Date

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Vitocrossal 300 CU3A 26 to 57 Service Startup
Check Power Supply Connection
Note: The line conductor “L “ and the neutral conductor
“N” must not be interchanged.
See wiring diagram on page 94 in section entitled
“Additional Information”.
IMPORTANT
In Canada all electrical wiring is to be done in accordance
with the latest edition of CSA C22.1 Part 1 and/or local
codes. In the U.S. use the National Electrical Code ANSI/
NFPA 70. The heating contractor must also comply with
both the Standard for Controls and Safety Devices for
Automatically Fired Boilers, ANSI/ASME CSD-1.
An external accessories connection modules are
integrated into the Vitocrossal 300 CU3A boiler, which
requires a 120VAC power supply from a wall receptacle
(15A fuse protected).
Refer to the Installation Instructions shipped with the
boiler.
Voltage range
The voltage at connector 40 of the boiler control must be
120V (see wiring diagram).
Neutral conductor
The electrical power supply must have a neutral
conductor.
Designating Heating Circuits
In the delivered condition, the heating circuits are
designated "Heating circuit 1", "Heating circuit 2" and
"Heating circuit 3" (if installed).
If the system user prefers, the heating circuits can be
designated differently to suit the specific system.
To enter names for heating circuits:
Refer to the Operating Instructions
Setting High Altitude
In the factory default setting, the boiler is equipped to
operate in altitudes of up to 5,000 ft. (1,500 m).
Altitude can be set using coding address 93:
(in coding level 2 General).
- Coding 11:9 must be set in order to unlock coding 93:.
- 93:0 is reserved for altitudes up to 5000 ft. (1500 m).
- 93:6 must be set for altitudes from 5000 ft. (1500 m).
to 10000 ft. (3000 m)
- Setting back to 93:0 turns off the high altitude
function.
IMPORTANT
Do not set or use coding addresses 93:1 to 93:5.
- After setting coding address 93:, set coding address 11:0
- The program is automatically disabled after 20 minutes.

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Gas type conversion
1. Set adjusting screw Aon the gas valve to “2”.
2. Turn ON/OFF switch “8” ON.
3. Select the gas type in coding address “82”.
- Call up code 2.
- “General”
- In coding address “11”, select value “9”.
- In coding address “82”, select value “1” (LPG
operation).
- Set code “11” value unequal “9”.
- End service functions.
4. Open the gas shut-off valve
5. Affix fuel conversion label supplied with the fuel
conversion kit as shown in the fuel conversion kit
instructions.
Convert Fuel Type to LPG
Startup
Select Gas Type
Note: the Vitocrossal 300 CU3A boiler is factory set to
operate with natural gas . See following subsection
for conversion instructions to liquid propane gas.
1. Ensure that the fuel type listed on the boiler rating
plate is the correct type for the installation being
attempted.
2. Record fuel type in Maintenance Record on page 106.
The Vitocrossal 300 CU3A boiler is for use with gases
whose characteristics fall within the following ranges.
Do not use any other types of gas.
Natural gas Liquid propane gas
Heating value (gross) Btu/ft3970 to 1100 2466 to 2542
Specific gravity 0.57 to 0.70 1.522 to 1.574
Ultimate carbon dioxide (CO2) % 11.7 to 12.2 13.73 to 13.82

15
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Vitocrossal 300 CU3A 26 to 57 Service Startup
1. To measure static and/or running pressure remove
boiler enclosure panel as indicated page 11 in these
instructions.
2. Close gas shutoff valve (field supplied).
3. Loosen screw at inlet gas pressure port Aon the
gas combination valve, do not remove completely.
Connect manometer.
4. Open the gas shutoff valve.
5. Measure static pressure. Values must be:
14 “w.c. maximum for NG
14 “w.c. maximum for LPG
6. Enter measured value into Maintenance Record on
page 106 in this manual.
7. Start up boiler, using the ON/OFF switch “8” on the
boiler control.
Note: Flip up lower orange cover to access the ON/
OFF switch.
8. Measure the running pressure; value must be:
Note: Use suitable measuring instruments calibrated
with a minimum resolution of 0.04 “w.c. for
measuring the running pressure.
9. Enter gas type into Maintenance Record on page 106
in this manual.
10. Switch off the ON/OFF switch “8” on the boiler
control, close the gas shut-off valve, remove the
manometer and re-tighten the screw at inlet gas
pressure port A.
Measure Static Pressure and Running Pressure
A CO2measurement (see page 25) must be taken before
and after working on gas appliances to eliminate risks to
health and to guarantee the satisfactory condition of the
system.
The burner is automatically ignited and starts operation
after a safety time has elapsed. During initial start-up,
the unit may indicate a fault because of air in the gas
supply pipe (especially for liquid propane gas). After
approx. 5 seconds, press the ”R” button to reset the
burner. The ignition procedure is repeated. This boiler
employs a direct spark ignition system.
WARNING
Ensure that there is no open flame in the room. WARNING
Never purge a gas line into a combustion chamber.
Never use matches, candles, flame, or other sources of
ignition for purpose of checking leakage. Use a soap and
water solution to check for leakage. A failure to follow
this warning could result in fire, explosion, personal
injury or death.
IMPORTANT
IMPORTANT
Running supply pressure with Corrective action
NG LPG
under 4 ”w.c. under 4 ”w.c. Do not start the boiler.
Notify your gas supply
utility or LPG supplier.
4 to 14 “w.c. 10 to 14 “w.c. Start up boiler.
over 14 “w.c. over 14 “w.c. Do not attempt
adjustment. Call local
gas utility to decrease
pressure or install up
stream gas pressure
regulator. Boiler valve
must not be exposed to
pressure over 14 ”w.c.

Vitocrossal 300 CU3A 26 to 57 Service
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16
Setting the Maximum Output
You can limit the maximum output for heating operation.
The limit is set via the modulation range. The max.
adjustable output is limited upwards by the boiler coding
card.
1. Press OK and simultaneously for approx. 4 sec.
2. “Service functions”
3. “Max. output”
4. “Change?” Select “Yes”. A value flashes on the
display (e.g. “85”). In the delivered condition,
this value represents 100 % of rated output.
5. Set the required value.
Startup
Check All Primary and Secondary Circuit Connections for Leaks
Check heating system and domestic hot water
connections (if applicable). Ensure all connections
are pressure tight. Correct any leaks found on fittings,
pumps, valves, etc.
CAUTION
Ensure all joints of gas line are pressure tight and that
gas valves do not leak when under normal operating
pressure (use approved leak detection liquid).
WARNING
The gas supply piping must be leak tested before placing
the boiler in operation.
WARNING
Escaping gas leads to a risk of explosion.
Check gas equipment for tightness.
Note: For the tightness test, use only suitable and
approved leak detecting agents and devices.
Leak detecting agents with unsuitable contents
(e.g. nitrites, sulphides) can lead to material
damage. Remove residues of the leak detecting
agent after testing.
Check Gas Pipes and Fittings for Leaks

17
5673 649 - 03
Vitocrossal 300 CU3A 26 to 57 Service
Legend
AFlue gas test port
Checking the Direct Vent (coaxial) System Tightness
Perform Combustion Analysis
A CO2measurement (see page 25) must be taken before
and after working on gas appliances to eliminate risks to
health and to guarantee the satisfactory condition of the
system.
Record the measured combustion values in the sequence
stated in the Maintenance Record on page 106 in this
manual.
IMPORTANT
Viessmann strongly recommends that the heating
contractor perform a simplified leak test during boiler
start-up. For this purpose it is sufficient to measure the
CO2concentration of the combustion air in the coaxial
gap of the air intake pipe adaptor. The vent pipe is
considered sufficiently leak-proof if a CO2concentration
in the combustion air no higher than 0.2% or an O2
concentration no lower than 20.6% is measured.
If higher CO2values or lower O2values are measured,
check venting system thoroughly.
Note: This measurement can be taken at the flapper A
located on the air inlet pipe located just prior to
the burner.
Startup
Legend
AAir inlet flapper

Vitocrossal 300 CU3A 26 to 57 Service
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18
Sequence of Operation and Potential Faults During Each Startup Cycle
Function sequence and possible faults
For further details on faults, see page 78.
Startup

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Vitocrossal 300 CU3A 26 to 57 Service
Removing the Burner and Checking the Burner Gasket
1. Switch OFF the main power supply and the ON/OFF
switch at the control unit.
2. Close the gas shut-off valve and safeguard against
reopening.
3. Pull power cables from fan motor H, gas valve Cand
ionization electrode D. Pull plug G.
4. Undo fitting on gas supply pipe Eand pull ventilation
air adaptor A.
5. Undo four nuts Band remove burner F, then hook
it into its service retainer L.
Note: Prevent damage to the burner. Always hook
the burner into its service retainer.
6. Check burner gasket Kfor possible damage;
replace if necessary. The burner gasket should be
replaced every 2 years.
Service
Placing the Burner Door in the Service Retainer
CAUTION
To avoid damage to the burner, do not lay burner on its
dome matrix or touch the burner mesh.
Failure to heed this caution may cause damage to the
burner, which may lead to improper operation.

Vitocrossal 300 CU3A 26 to 57 Service
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20
Checking Burner Mesh Assembly and Refractory
Service
Replace the burner mesh assembly if the wire mesh is
damaged.
1. Remove electrodes A.
2. Undo four nuts Dand remove fan with gas valve C.
3. Release three nuts Band remove burner mesh
assembly H.
4. Remove refractory Fwith thermal insulating mat E.
5. Remove old burner mesh assembly gasket G.
6. Check refractory F for damage and replace, if
required.
7. Insert thermal insulating mat Eand refractory F
according to the electrode position.
Note: Observe the positioning aid on the refractory.
8. Insert new burner mesh assembly Hwith new
gasket Gand secure with three nuts.
Torque: 3.7 lbf.ft (5 Nm).
9. Fit the fan with the gas valve. Torque: 3.7 lbf.ft (5 Nm).
1. Check the electrodes for wear and contamination.
2. Clean the electrodes with a small brush (not with a
wire brush) or sandpaper.
3. Check the electrode gaps. If the gaps are not as
specified or the electrodes are damaged, replace
and align the electrodes together with new gaskets.
Tighten the electrode fixing screws with a torque of
1.8 lbf.ft (2.5 Nm).
Legend
AIgnition electrodes
BIonization electrode
CUp to 35 kW
DFrom 45 kW
CAUTION
Do not damage wire gauze of the burner head.
Checking and Adjust the Ignition and Ionization Electrodes