Viessmann VITOCROSSAL 300 Operating instructions

for use by heating contractor
Please file in Service Binder
Product may not be exactly as shown
5285 875 - 04 01/2016
Service Instructions
VITOCROSSAL 300
Vitocrossal 300
CT3 Series
Gas-fired condensing boiler
Heating input: 638 to 3361 MBH
187 to 985 kW
Read and save these instructions for
future reference.
IMPORTANT
Vitocrossal 300, CT3 boiler
with Vitotronic control

Vitocrossal 300, CT3 Series Service
5285 875 - 04
2
Safety, Installation and Warranty Requirements
Safety
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).
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 in the “Service Instructions” manual.
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 section entitled “Combustion
air supply” and “Venting information”
in this manual.
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 this manual.
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
Information” in this manual. All
products of combustion must be
safely vented to the outdoors.
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 Safety Requirements”.
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 section
entitled “Mechanical Room”.
in this manual.
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.
Warranty
Information contained in this and
related product documentation must
be read and followed. Failure to do
so renders the warranty null and void.

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Vitocrossal 300, CT3 Series Service Safety
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.
HFiberglass 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.
Suppliers of fiberglass wool products recommend the
following precautions be taken when handling these
materials:
Precautionary measures
- 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.
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.
HHazardous materials
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.

4
Page
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Vitocrossal 300, CT3 Series Service
Table of Contents
Safety, Installation and Warranty Requirements..............2
Product documentation...........................................2
Licensed professional heating contractor...................2
Contaminated air ...................................................2
Advice to owner ....................................................2
Warranty ..............................................................2
Carbon monoxide...................................................2
Fresh air ...............................................................2
Equipment venting .................................................2
Fiberglass wool and ceramic fiber materials...............3
Suppliers of ceramic fiber products recommend
the following first aid measures: ..............................3
Precautionary measures..........................................3
First aid measures..................................................3
Hazardous materials ...............................................3
Important Regulatory and Safety
Requirements.............................................................6
Instructing the system user .....................................6
Initial start-up........................................................6
Working on the equipment ......................................6
Technical literature ................................................6
About these Instructions .............................................7
Necessary Tools.........................................................8
Tools ...................................................................8
Cleaning supplies ...................................................8
Testing/Analysis equipment.....................................8
Technical information .............................................8
Replacement parts .................................................8
Customer Site Information...........................................9
Site......................................................................9
Boiler ...................................................................9
Burner ..................................................................9
Installing Contractor...............................................9
Product Information..................................................10
Shut Down Heating System.......................................10
Check Pressure Relief Rating......................................10
Safety
General Information

Table of Contents
5
Page
5285 875 - 03
Vitocrossal 300, CT3 Series Service
Inspection and Maintenance
Additional Information
Dispose of Condensate .............................................11
Check Flue Gas Damper ............................................11
Check Venting Connection ........................................11
Start up Heating System ...........................................12
Reduce Pulsation Noises ...........................................13
Open Combustion Chamber Door ...............................13
Clean Combustion Chamber and Heat Exchanger
Surfaces .................................................................14
Clean Observation Port in Combustion Chamber Door ...15
Check all Connections and Sensor Well for Leaks .........16
Check Proper Operation of Low Water Cut-off .............16
Check Proper Expansion Tank and System Pressures ....16
Check Flue Gas Collector for Leaks.............................17
Close Combustion Chamber Door ...............................17
Check Thermal Insulation ..........................................18
Check Viessmann Mixing Service Valve for Proper
Operation and Leaks .................................................18
Adjust Burner ..........................................................18
Check Separate Heating System Controls ...................18
Check for Proper DHW Production..............................18
Maintenance Schedule ..............................................19
Frequency...........................................................19
Performed by ......................................................19
Service...............................................................19
Danger of Freezing ...................................................21
Long Periods of Shut-down........................................21
Water Quality ..........................................................21
Technical Data.........................................................22
Parts List.................................................................24
When ordering replacement parts...........................24
Parts ..................................................................24
Maintenance Record .................................................30
Maintenance/Service ............................................30

Vitocrossal 300, CT3 Series Service
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Safety
Important Regulatory and Safety Requirements
Working on the equipment
The installation, adjustment, service, and maintenance
of this boiler must be performed 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.
Note: Please carefully read this manual prior to attempting
installation. 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.
Viessmann offers 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.
Note: The completeness and functionality of field supplied
electrical controls and components must be verified
by the heating contractor. This includes low water
cut-offs, flow switches (if used), staging controls,
pumps, motorized valves, air vents, thermostats, etc.
Technical literature
Literature for the Vitocrossal 300 CT3 boiler:
- Technical Data Manual
- Installation Instructions
- Service Instructions
- Operating Instructions and User’s Information Manual
Note: 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.
Additional applicable literature:
- Viessmann boiler controls manuals
Instructing the system user
The installer of the system is responsible to ensure the
system operator/ultimate owner is made familiar with the
functioning of the system, its activation, and its shut-
down.
Note: The following topics must be covered:
Proper system operation sequence.
Explain the equipment as well as the need for
combustion air.
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.
Initial start-up
Initial start-up must be performed by a qualified heating
contractor. Completion of the Maintenance Record by the
heating contractor is also required.
Note: The Maintenance Record is located on page 30 of
this manual.

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Vitocrossal 300, CT3 Series Service General Information
About these 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.

Vitocrossal 300, CT3 Series Service
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8
Necessary Tools
General Information
Tools
HAssortment of flathead and Phillips screwdrivers
HPipe wrenches
HOpen-ended wrenches
HPipe sealant
HAssortment of Allen keys
HFlashlight
HApproved leak detection fluid for natural gas and
propane gas
Cleaning supplies
HHand brush
HCleaning/service brush
HVacuum cleaner
HRags
Testing/Analysis equipment
(use only calibrated equipment)
HFlue gas analyzer to measure % CO2or O2
(i.e. Bacharach fluid samplers or a suitable electronic
analyzer)
HMultimeter to measure 0 - 120VAC, 0 - 20 amps AC,
and 0 - 20 microamps DC
HPressure gage to measure gas pressure 0 - 28 ”w.c.
(a non-electric Magnehelicrpressure gage may also be
used)
HCarbon monoxide measuring equipment (0 - 400 ppm)
HBacharach calculator or suitable tables to calculate
efficiency
HStack thermometer 0 to 250°F (0 to 121°C)
Hdin. NPT male to ¼ in. barb adaptor fitting, as well as
tubing for pressure measurement
CAUTION
Use only original Viessmann components when replacing
defective parts. Installation of incorrect replacement
parts can cause hazardous operation and will void
warranty.
Technical information
The following is a list of literature applicable to the
Vitocrossal 300, CT3 boiler:
HInstallation Instructions
HService Instructions
HOperating Instructions and User’s Information Manual
For installation of the heating system, please refer also
to the technical literature of other System Technology
devices:
HInstallation Instructions for Viessmann boiler control
HInstallation Instructions for Viessmann indirect-fired hot
water storage tank(s)
HInstallation Instructions for burner and accessories
Replacement parts
The materials listed below are recommended to be on
hand for all service calls.
For a complete listing of replacement components, please
see Parts List starting on page 24 of these instructions.
Order replacement components from your Viessmann
distributor.

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Vitocrossal 300, CT3 Series Service
Customer Site Information
General Information
Site
Name:
Street:
City:
Tel.:
Boiler
Mfr.: Viessmann
Series:
Heating Input: MBH
Serial No.:
Burner
Mfr.:
Series:
Heating Input: MBH
Serial No.:
Installing Contractor
Firm:
Technician:
Address:
Tel.:
Installed on:
Please complete the information below.

Vitocrossal 300, CT3 Series Service
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10
Product Information
General Information
Shut Down Heating System
High efficiency gas-fired hot water condensing boiler.
For operation with modulating boiler water temperatures
in closed loop, forced circulation hot water heating
systems.
The Vitocrossal 300, CT3 boilers are CSA certified with
Weishaupt and Riello burners which must be used in
conjunction with this boiler series.
The proper burner size must be verified and the burner
must be adjusted so that the maximum input of the
appropriate boiler size is always observed and adjusted.
The gas burner must always be installed according to the
instructions provided by the burner manufacturer.
The boiler model selected should be based on an accurate
heat loss calculation of the building. The boiler selected
must be compatible with the connected radiation.
The Vitocrossal 300 boiler is suitable for a maximum
operating pressure of 30 psig and a maximum boiler water
temperature of 210°F (99°C).
The maximum hydrostatic test pressure is 45 psig.
1. Deactivate main power supply to heating system and
secure against accidental reactivation.
2. Disconnect fA plug from burner (where applicable).
3. Close main gas supply valve.
WARNING
Exposing the boiler to pressures and temperatures in
excess of those listed will result in damages, and will
render warranty null and void.
Check Pressure Relief Rating
The maximum allowable working pressure is 30 psig.
WARNING
There may be more than one electrical disconnect.
See Installation and Operating Instructions
for Vitotronic controls.
The Vitocrossal 300 boiler series is operated with
a Vitotronic control and microcomputer indoor/
outdoor control system for boiler operation without
low temperature limit. The control system must be
programmed for this type of operation.
This boiler does not require a flow switch.
This boiler is for natural gas or propane gas only.

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Vitocrossal 300, CT3 Series Service Inspection and Maintenance
Flue gas temperature gross
Boiler water return temperature
Amount of condensate
Flue gas temp
at full input
Flue gas temp
at partial load
Amount of
condensate
Dispose of Condensate
During the operation of the Vitocrossal 300 boiler,
the amount of condensate as per the diagram can be
expected. The values given are approximate amounts
occurring under practical conditions. Not included in the
chart is the amount of condensate occurring in the vent
pipe and chimney system.
The condensate from the chimney system can be
collected together with the condensate from the heating
boiler and be disposed of into a floor drain.
The condensate occurring will have between 3 and 4
on the pH scale. If local building requirements demand
neutralizing the condensate before disposal, contact
Viessmann Manufacturing Company Inc. for a correctly
sized neutralization tank. The treated condensate will
show pH values of between 6.5 and 9 and can then be
disposed of into the waste water system.
Note: The “amount of condensate” and the “flue gas
temperature gross” graphs are independent of each
other.
Check Flue Gas Damper
The flue gases contain a large amount of condensate.
The condensate pH value is usually between 3 and 4.
The flue gas temperatures depending on the boiler return
water temperature may be between 77°F and 257°F
(25°C and 125°C).
It is the responsibility of the manufacturer of the chimney
system or venting system that they must properly design
the venting system as well as select proper materials.
Check Venting Connection
CAUTION
The flue gas damper is adjusted at the time of start-up
commissioning.
Do not readjust. Any readjustments require confirmation
of flue gas analysis.
For handling the damper, see section
on pulsating noises on page 13.
If there are any questions in regards to the neutralization
of the condensate and/or to the venting of this
boiler series, contact your local Viessmann Sales
Representative.

Vitocrossal 300, CT3 Series Service
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12
Inspection and Maintenance
3. Maximum allowable working pressure is 30 psig.
4. Check and ensure that all ventilation is free of
obstructions and communicates freely into the
mechanical room.
5. Check the gas supply pressure (0 - 10 psig).
6. Check whether the cleaning opening on the flue outlet
is closed.
7. Review all gas piping, perform leak test and open
manual gas valve.
8. Ensure that all sensors are properly connected to the
Vitotronic control unit.
9. Switch ON the main power disconnect, the switch for
the heating circuit pump and the burner control
switch, in that order.
1. Check if all national and/or local rules and regulations
have been adhered to on this installation.
Do not attempt to start the boiler if you smell gas.
If you smell gas open windows and doors and call
your gas supplier immediately from a neighbor’s
phone.
Do not touch any electrical switches.
Extinguish any open flame.
2. Check system for proper water fill (cold fill pressure).
Make sure that the complete system is properly
vented hydronically. If installed, adjust automatic
feed valve for proper fill pressure. Never burn
garbage or paper in the combustion chamber or leave
combustible materials around the heating system.
Start up Heating System
CAUTION
Do not tamper with the unit or controls.
CAUTION
The start-up must be performed by a qualified service
mechanic.
Reference operating instructions for control unit,
burner and neutralization system. Also reference
service instructions of control unit, as well as
burner manufacturer’s documentation.
IMPORTANT
Observe boiler temperature. Reset fixed high limit
if required.
See burner manufacturer’s
operating instructions.
12. Check for proper operation of all circulating pumps,
mixing valves, thermostats, zone valves, and any
additional operating control function.
13. Check adjustable high limit (AHL) aquastat on
Vitotronic control by dialing it to a setting below the
boiler water temperature. The gas burner must
deactivate. Turning the dial back to a setting higher
than the present boiler water temperature must result
in reactivation of gas burner. To adjust the dial on the
adjustable temperature high limit on the Vitotronic
control refer to the Vitotronic instruction literature.
14. Cycle boiler on/off with the operating control to verify
proper operation.
15. Check the function of the neutralization unit (if
installed).
16. Inspect all gaskets, unions and seals for tightness.
A few days after start-up, return and tighten bolts
on combustion chamber door, as well as all clean-out
and inspection openings on the boiler to ensure tightness.
IMPORTANT
A system start-up report including a burner calibration
report must be handed to the owner of the system.
See burner data for details.
10. The start-up of the system will be automatically
initiated by the Vitotronic control.
The gas burner should be calibrated immediately for
maximum input and also for combustion results.
11. Once system water is heated, deactivate circulating
pump/boiler and vent system of any remaining
air within piping, radiation and boiler.

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Vitocrossal 300, CT3 Series Service Inspection and Maintenance
Reduce Pulsation Noises
Gas-tight (positive pressure) flue systems may create
pulsation noises, irrespective of the boiler, burner or flue
gas system make. Pulsation noises may be reduced by
rotating the damper fitted into the flue outlet (during start-
up only).
1. Loosen M 10 nut Ain lever B of damper C.
2. Adjust the lever until all pulsating noises have ceased
(the lever mirrors the damper position).
3. Lock the damper with the M 10 nut.
4. Readjustment of burner settings is required.
CAUTION
Do not put any tools or other objects into the
combustion chamber.
1. Remove the gas supply pipe.
2. Loosen the screws on the boiler door and open it.
Open Combustion Chamber Door

Vitocrossal 300, CT3 Series Service
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Inspection and Maintenance
Clean Combustion Chamber and Heat Exchanger Surfaces
1. Ensure main power supply to equipment, the
heating system, and all external controls has been
deactivated. Take precautions in both instances to
avoid accidental activation.
2. Close all gas valves.
3. Allow boiler to cool if necessary (boiler should be at
room temperature).
4. Use a plastic covering to protect the burner door,
burner, and gas controls from water spray.
5. Open observation cover plate on the front of the
stainless steel flue gas collector located on the front
of the boiler. The observation opening is accessed by
first removing the bottom front enclosure panel.
6. Use a water hose to wash down stainless steel
combustion chamber and Inox-Crossal water heating
section (avoid water contact with rope material on
boiler combustion chamber door). Do not allow any
water to enter between pressure vessel and insulated
enclosure.
7. Direct garden hose into the flue gas collector at the
bottom of the boiler, washing any sediment from the
combustion chamber down the condensate drain.
Verify that all “P” traps on all condensate drain
lines are clear, and that water flows freely without
restriction or accumulation.
IMPORTANT
It is recommended to service, clean and inspect the
heating system at least once a year. Viessmann
recommends a service contract with a mechanical firm.
Neglected service on the unit presents a risk, service
and cleaning on a regular basis ensures that the unit will
operate at its peak efficiency with minimal emissions over
many years of operation.
IMPORTANT
Combustion residues coating the heat transfer surfaces
may cause an increased flue gas temperature and
therefore reduced efficiency. The flue gas temperature
increases by 90°F (50°C) with each 1/25 in. (1 mm)
accumulation.
Combustion
chamber door
Observation
port
Combustion
chamber
door bolts
Combustion
chamber
door bolts
CAUTION
The cleaning agent used must not contain any solvents
based on hydro-carbons.
IMPORTANT
Do not use any abrasive materials, such as wire brushes,
to clean stainless steel combustion chamber.
Use only soft nylon brushes or clean rags to wipe down
combustion chamber. Remove any loose debris.

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5285 875 - 04
Vitocrossal 300, CT3 Series Service Inspection and Maintenance
Clean Combustion Chamber and Heat Exchanger Surfaces (continued)
8. With a good light source (flash light, trouble light)
examine combustion chamber and flue gas collector
area for discoloration of the stainless steel.
If discoloration exists, an acid wash is recommended.
The recommended phosphoric acid-based cleaner
is Antox 73 E Plus. The recommended citric acid-based
cleaner is CitriSurft 3050 by Stellar Solutions Inc.
These cleaners are available at most welding supply
stores. Do not use any other chemical cleaner.
9. Lightly spray the cleaning agent onto the discolored
areas. Allow acid wash to work on stainless steel
surfaces for approx. 15 - 20 minutes, then rewash
combustion chamber with water. Repeat if necessary.
Observe detailed instructions supplied with cleaning
agent.
10. Secure observation cover plate on the front of the
flue gas collector.
11. Secure combustion chamber door to boiler.
Complete a gas leak test and verify proper operation
of all components.
CAUTION
Ensure that no cleaning agent is entering between the
pressure vessel and the insulation enclosure.
WARNING
Follow cleaning agent instructions.
Wear protective clothing/gloves as well as eyewear.
Check gaskets A and hose connection B for leaks.
Clean Observation Port in Combustion Chamber Door
IMPORTANT
Do not over tighten to avoid leaks and potential damage.

Vitocrossal 300, CT3 Series Service
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16
Inspection and Maintenance
Check all Connections and Sensor Well for Leaks
This diaphragm expansion vessel reduces the frequency
and severity of pressure fluctuations; the service life
of the circulating pump is improved and therefore
the operational reliability and service life of system
components increased.
1. Drain system or close cap valve on the diaphragm
expansion tank and reduce the pressure until the
pressure gage indicates “0”.
2. Cold static 60°F (15.5°C) water fill pressure must
equal diaphragm expansion tank pressure.
IMPORTANT
The diaphragm expansion tank must be able to hold the
heating water expansion volume inside the boiler, and
must be properly sized for the system.
CAUTION
Only open the heating water connections after the boiler
has been depressurized. Only drain the boiler with a
vacuum pump when the boiler air vent valve is open.
IMPORTANT
Carry out this test on a cold system.
CAUTION
Carry out all check in accordance with the expansion tank
manufacturer’s instructions. Limit pressure fluctuations
to the lowest possible differential. Cyclical pressure
fluctuations and greater pressure differentials indicate a
system fault. Immediately remedy such faults, otherwise
other heating system components may become faulty.
CAUTION
Damage on boiler or other system components may
result if these recommendations are not followed.
1. Remove cap Afrom the back of the boiler.
2. Check sensor well B for leaks.
3. Reinstall cap.
Check Proper Operation of Low Water Cut-off
Check Proper Expansion Tank and System Pressures
Observe the detailed test instructions by the
manufacturer.
Reference expansion tank manufacturer’s
instructions.
AB

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Vitocrossal 300, CT3 Series Service Inspection and Maintenance
Check Flue Gas Collector for Leaks
1. Tighten the screws on the boiler door evenly and
diagonally. See drawing on the left for tightening
sequence.
2. Install the gas supply pipe.
CAUTION
Check all gas connections for tightness.
Close Combustion Chamber Door
1. Visually check the gasket through clean-out opening
Aon the flue gas collector. Traces of condensate on
the outside of the flue gas collector indicate a leak.
2. If necessary, retighten the gaskets using clamping
clips B.

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18
Inspection and Maintenance
Check Viessmann Mixing Service Valve for Proper Operation and Leaks
1. Remove the motorized lever from the mixing valve
handle.
2. Check mixing valve for ease of operation.
3. Check mixing valve for leaks.
Replace the O-rings if the mixing valve leaks.
4. Snap the motorized lever back into place.
Follow manufacturer’s instructions
supplied with burner.
Adjust Burner
Check Separate Heating System Controls
Check for Proper DHW Production
The input of the burner used with the Vitocrossal 300
boiler must be adjusted so that the maximum boiler input
of the particular boiler model is not exceeded.
The burner must also be adjusted for proper combustion
results. CO2values between 9 and 10% are possible.
In case additional controls are installed
in the boiler room, e.g. control aquastats, mixing valves,
controls etc., please observe their respective operating
instructions.
The Vitocrossal 300 boiler may be used to supply
domestic hot water heating by means of an indirect-fired
hot water storage tank. The appropriate connections
to the boiler must be made, as well as the correct size
circulating pump must be used. The control circuit
to provide domestic hot water is already provided within
the Vitotronic control (motor contactor may be required
in some instances). Please contact your local Viessmann
Sales Representative for details.
Check Thermal Insulation
Check thermal insulation fit and adjust if necessary.

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Vitocrossal 300, CT3 Series Service Inspection and Maintenance
Maintenance Schedule
The following is an overview of scheduled service steps.
Regular service work ensures reliable, energy-efficient,
and environmentally friendly operation.
Frequency Performed by Service
Monthly Owner /
Operator
Check the system pressure frequently.
Ensure proper operation of the boiler control. Refer to operating instructions of
control.
Inspect all seals; retighten or replace as necessary.
Ensure an adequate supply of combustion air and ventilation air into and out of the
mechanical room is being maintained at all times.
Ensure that nothing is obstructing the flow of combustion - ventilation air, and no
chemicals, garbage, gasoline, combustible materials, flammable vapors, or liquids
are stored, not even temporarily, in the vicinity of the boiler.
Check for water on the floor from the discharge pipe of pressure relief valve or any
other pipe, pipe joint, valve, or air vent.
Test pressure relief valve and check for proper operation. See instructions attached
to pressure relief valve.
Check all operational high limits for proper operation.
Check for proper operation of the condensate neutralization system (if used).
Check the condition and fill status of the neutralization media.
Check the pH value of the flue gas condensate (min. 6.5).
Check for moisture water on external vent pipe joints and appearance of ice on the
vent pipe or chimney outlet in the winter time.
IMPORTANT
Keep boiler and boiler room clear and free from combustible
materials, gasoline and other flammable vapors and liquids.
Do not obstruct the flow of combustion and ventilation air.
All inspection, maintenance, and service must be performed
by a qualified heating contractor.
IMPORTANT
The boiler must be cleaned at least once a year by
a qualified heating contractor or service agency.

Vitocrossal 300, CT3 Series Service
5285 875 - 04
20
Inspection and Maintenance
Maintenance Schedule (continued)
Frequency Performed by Service
Annually Owner /
Operator
Ensure service work/test is conducted at least annually by qualified personnel,
and that any deficiencies are corrected immediately.
Heating
Contractor
Test functionality of safety high limits.
Test burner with burner accessories according to their corresponding maintenance
checklist.
Test and establish proper chemical makeup of system water.
Check flue pipe condition, chimney connection and chimney itself.
Check pressure relief valve and system pressure, and verify proper operation.
Check heating pipe joints, valves, air vents, etc. System leaks must be corrected
immediately to avoid further defects.
The cause of defect must also be determined in order to avoid further problems.
Check for proper combustion air supply and ventilation to boiler / mechanical room.
Test high limits by dialing lower settings, switching burner on/off to verify
functioning of same. Test low water cut-off, check and verify proper function
according to manufacturer’s instructions.
When circulating pump is field-installed or existing, check requirements
for maintenance or lubrication according to manufacturer’s specifications.
Check for gas-tight connection of gas piping, unions, gas valve and manifold.
Check proper ignition on oil or gas burner operation.
Combustion test must be performed by a qualified heating contractor.
Periodically Heating
Contractor
Ensure functionality of low water cut-offs, including flushing of float types (if used)
during operation, based on supplier’s instructions.
Inspect low- and/or high pressure gas switch (if used).
Inspect main burner flame and follow burner manufacturer’s instruction manual
for detailed service and maintenance guidelines. Manual shipped with burner.
All boilers and the boiler room must be kept free of high dust levels, high humidity,
aggressive vapors and/or chemicals containing chlorine.
Ensure proper boiler room ventilation.
Valves, fittings and pipes not pressure tight must be repaired.
Combustion chamber door, clean-out opening covers, and flanges may need to be
retightened and resealed. Do not over tighten.