A.O. Smith VF VB 500 User manual

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WARNING: If the information in this
manual is not followed exactly, a re or
explosion may result causing property
damage, personal injury or loss of life.
— Do not store or use gasoline or other
ammable vapors and liquids in the
vicinity of this or any other appliance.
— WHAT TO DO IF YOU SMELL GAS:
• Do not try to light any appliance.
• Do not touch any electrical switch; do
not use any phone in your building.
• Immediately call your gas supplier
from a neighbor’s phone. Follow the
gas supplier’s instructions.
• If you cannot reach your gas supplier,
call the re department.
— Installation and service must be
performed by a qualied installer,
service agency or the gas supplier.
PRINTED 0411 320857-000
USER’S MANUAL
MODELS:
VB/VW-500, 750 AND 1000
SERIES 200/201
GAS-FIRED POWER BURNER
COPPER BOILERS FOR HYDRONIC HEATING
AND HOT WATER SUPPLY
• Installation
• Operation
• Maintenance
• Limited Warranty
500 Tennessee Waltz Parkway
Ashland City, TN 37015
www.hotwater.com

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SAFE INSTALLATION, USE AND SERVICE
APPROVALS
The proper installation, use and servicing of this boiler is extremely important to your safety and the safety of others.
Many safety-related messages and instructions have been provided in this manual and on your boiler to warn you and others of a
potential injury hazard. Read and obey all safety messages and instructions throughout this manual. It is very important that the
meaning of each safety message is understood by you and others who install, use, or service this boiler.
DANGER indicates an imminently
hazardous situation which, if not avoided,
will result in injury or death.
This is the safety alert symbol. It is used to alert you to
potential personal injury hazards. Obey all safety
messages that follow this symbol to avoid possible
injury or death.
WARNING indicates a potentially hazardous
situation which, if not avoided, could result
in injury or death.
CAUTION indicates a potentially hazardous
situation which, if not avoided, could result in
minor or moderate injury.
CAUTION used without the safety alert
symbol indicates a potentially hazardous
situation which, if not avoided, could result in
property damage.
WARNING
CAUTION
CAUTION
DANGER
All safety messages will generally tell you about the type of hazard, what can happen if you do not follow the safety message, and how
to avoid the risk of injury.
The California Safe Drinking Water and Toxic Enforcement Act requires the Governor of California to publish a list of substances known
to the State of California to cause cancer, birth defects, or other reproductive harm, and requires businesses to warn of potential
exposure to such substances.
This product contains a chemical known to the State of California to cause cancer, birth defects, or other reproductive harm. This
appliance can cause low level exposure to some of the substances listed in the Act.
IMPORTANT DEFINITIONS
• Qualified Installer: A qualified installer must have ability equivalent to a licensed tradesman in the fields of plumbing,
air supply, venting and gas supply, including a thorough understanding of the requirements of the National Fuel Gas
Codeasitrelatestotheinstallationofgasredboilers.Thequaliedinstallermusthaveathoroughunderstandingofthisinstructionmanual.
• Service Agency: A service agency also must have ability equivalent to a licensed tradesman in the fields of plumbing,
air supply, venting and gas supply, including a thorough understanding of the requirements of the National Fuel Gas
Code as it relates to the installation of gas fired boilers. The service agency must also have a thorough
understanding of this instruction manual, and be able to perform repairs strictly in accordance with the service guidelines
provided by the manufacturer.
• Gas Supplier: The Natural Gas or Propane Utility or service who supplies gas for utilization by the gas burning
appliances within this application. The gas supplier typically has responsibility for the inspection and code approval of
gas piping up to and including the Natural Gas meter or Propane storage tank of a building. Many gas suppliers also
offer service and inspection of appliances within the building.

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GENERAL SAFETY

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SAFE INSTALLATION, USE, AND SERVICE .............................................................................................................................................. 2
GENERAL SAFETY.......................................................................................................................................................................................... 3
TABLE OF CONTENTS .................................................................................................................................................................................. 4
Installation Requirements for the Commonwealth of Mass ........................................................................................................................ 5
Wiring Diagram ..............................................................................................................................................................................................6-7
Schematic Diagram .......................................................................................................................................................................................... 8
Lighting and Operating Instructions ............................................................................................................................................................... 9
Water Temperature Regulation...................................................................................................................................................................... 10
Control System .......................................................................................................................................................................................... 10-11
Operating Sequence....................................................................................................................................................................................... 11
UIM Operating Procedures............................................................................................................................................................................ 12
Operating Setpoint Adjustment Procedure................................................................................................................................................... 14
TROUBLESHOOTING IGNITION SYSTEM ................................................................................................................................................ 16
Troubleshooting Gas Valve....................................................................................................................................................................... 17
PREVENTATIVE MAINTENANCE................................................................................................................................................................. 17
Main Burners.............................................................................................................................................................................................. 17
Relief Valve ................................................................................................................................................................................................ 18
Combustion Air Filter................................................................................................................................................................................. 18
Blower Compartment ................................................................................................................................................................................. 18
Burner Maintenance................................................................................................................................................................................... 18
Condensate Removal System.................................................................................................................................................................. 18
Venting Maintenance ................................................................................................................................................................................. 19
Heat Exchanger Preventive Maintenance............................................................................................................................................... 19
Tube Cleaning Procedure ....................................................................................................................................................................... 19
REPLACEMENT PARTS................................................................................................................................................................................ 19
LIMITED WARRANTY.................................................................................................................................................................................... 23
CONTENTS
INTRODUCTION
This design complies with the current edition of the ANSI
Z21.13 low-pressure boiler standard.
Compliance under this standard implies that when the boiler
underwent test, the gas manifold and control assembly provided
on the boiler met safe lighting and other performance criteria.
Detailed installation diagrams are found in this manual. These
diagrams will serve to provide the installer a reference for the
materials and methods of piping necessary. It is essential that
all water, gas piping and wiring be installed as shown on the
diagrams. You should thoroughly read and understand this
manual before installation and/or operation of this boiler.
The factory warranty will be void if the boiler(s) have been
improperly installed or operated.
AL 29-4C®is a registered trademark of Allegheny Ludlum
Corporation.
In addition to these instructions, the boiler(s) shall be installed in
accordance with those installation regulations in force in the local
area where the installation is to be made. These shall be carefully
followed in all cases. Authorities having jurisdiction should be
consulted before installations are made.
In the absence of local codes, the installation must comply with
the current editions, as follows:
In the United States:
The National Fuel Gas Code, ANSI Z223.1/NFPA 54 and the
National Electric Code, NFPA 70.

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For all side wall terminated, horizontally vented power vent, direct vent, and power direct vent gas fueled water heaters
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seven(7)feetabovenished
gradeintheareaoftheventing,includingbutnotlimitedtodecksandporches,thefollowingrequirementsshallbesatised:
INSTALLATION OF CARBON MONOXIDE DETECTORS At the time of installation of the side wall horizontal vented gas fueled
equipment,theinstallingplumberorgasttershallobservethatahardwiredcarbonmonoxidedetectorwithanalarmandbatteryback-up
isinstalledontheoorlevelwherethegasequipmentistobeinstalled.Inaddition,theinstallingplumberorgastter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 sidewall horizontal vented gas fueled equipment. It shall be the responsibility of the property owner to secure
theservicesofqualiedlicensedprofessionalsfortheinstallationofhardwiredcarbonmonoxidedetectors.
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oorlevel.
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 that during said thirty (30) day period, a battery
operated carbon monoxide detector with an alarm shall be installed.
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CSAcertied.
SIGNAGE Ametalorplasticidentication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.”
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.
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.
MANUFACTURER REQUIREMENTS - GAS EQUIPMENT VENTING SYSTEM PROVIDED When the manufacturer of Product
Approved side wall horizontally vented gas equipment provides a venting system design or venting system components with the
equipment, the instructions provided by the manufacturer for installation of the equipment and the venting system shall include:
1. Detailed instructions for the installation of the venting system design or the venting system components; and
2. A complete parts list for the venting system design or venting system.
MANUFACTURER REQUIREMENTS - GAS EQUIPMENT VENTING SYSTEM NOT PROVIDED When the manufacturer
ofaProductApprovedsidewallhorizontallyventedgasfueledequipmentdoesnotprovidethepartsforventingtheue
gases,butidenties“specialventingsystems,”thefollowingrequirementsshallbesatisedbythemanufacturer:
1. The referenced “special venting system” instructions shall be included with the appliance or equipment installation instructions; and
2. The “special venting systems” shall be Product Approved by the Board, and the instructions for that system shall include a
parts list and detailed installation instructions.
A copy of all installation instructions for all Product Approved side wall horizontally vented gas fueled equipment, all venting
instructions, all parts lists for venting instructions, and/or all venting design instructions shall remain with the appliance or
equipment at the completion of the installation.
INSTALLATION REQUIREMENTS FOR THE COMMONWEALTH OF MASSACHUSETTS

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CONNECTION DIAGRAM

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FIGURE 1. - SCHEMATIC DIAGRAM
VB/VW-500, 750 & 1000 SCHEMATIC DIAGRAM

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LIGHTING & OPERATION INSTRUCTIONS FOR MODELS VB/VW 500, 750 AND 1000:

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The boiler should be located in an area that is inaccessible to
the general public.
TABLE 1. Risk of Scalds.
Water Temperature Time to Produce 2nd & 3rd Degree
Burns on Adult Skin
Over 170°F (77°C) Nearly instantaneous
160°F (71°C) About 1/2 second
150°F (66°C) About 1-1/2 seconds
140°F (60°C) Less than 5 seconds
130°F (54°C) About 30 seconds
120°F (49°C) or less More than 5 minutes
SHOULD OVERHEATING OCCUR OR THE GAS SUPPLY FAIL
TO SHUT OFF, TURN OFF THE MAIN MANUAL GAS SHUTOFF
VALVE TO THE APPLIANCE.
The operating temperature of the boiler must be maintained
as follows:
• 120°F (49°C) or higher inlet water temperature to the boiler.
• 20°F (11°C) differential between the boiler’s inlet and
outlet (e.g. 120°F [49°C] inlet, 140°F [60°C] outlet
minimum design temperatures).
If the inlet water temperature into the boiler is less than
120°F (49°C), adjustments on the water bypass are needed.
Please contact your A.O. Smith qualified service agent.
CONTROL SYSTEM
The EMC modulation control system is a fully integrated, state
of the art electronic control system. It consists of sensors, output
devices, a power switch, a 24VAC transformer, wiring, and the
following printed circuit boards:
• ModulationControlBoard(MCB)
• PowerDistributionBoard(PDB)
• UserInterfaceModule(UIM)
The MCB contains circuitry for both master control and ame
control. Dip switches on the MCB are used to configure the
system. The User Interface Module (UIM) communicates with the
user through a set of touch pads and a 4-line, 20-character LCD
display. The PDB provides connection points for input power, the
water pump, and the transformer. It also distributes power to the
system and contains the system fuses.
The MCB also contains an external communications system to allow
for connection to a PC, a modem, an EMS system, or something
similar. Through this connection, multiple boilers can also be
linked together. CAUTION: The internal communications cables
should never be connected to the external communications
connectors, and vice-versa.
There are several microcontrollers used on the boards. These
control the temperature and ignition control functions for
the boiler. Inherent in the design are the normal operating
WATER TEMPERATURE REGULATION
HOT WATER CAN SCALD: Boilers are intended to produce hot
water. Water heated to a temperature which will satisfy space
heating, clothes washing, dish washing and other sanitizing needs
can scald and permanently injure you upon contact. Some people
are more likely to be permanently injured by hot water than others.
Theseincludetheelderly,children,theinrmorphysically/mentally
disabled.Ifanyoneusinghotwaterinyourhometsintooneoftheses
groupsor ifthereisalocal codeorstatelawrequiringaspecic
temperature water at the hot water tap, then you must take special
precautions. In addition to using the lowest possible temperature
settingthatsatisesyourhotwaterneeds,ameanssuchasamixing
valve should be used at the hot water taps used by these people or
at the hot water supply tank. Mixing valves are available at plumbing
supply or hardware stores. Follow the manufacturer’s instructions
for installation of the valves. Before changing the thermostat setting
on the hot water system controller, see Table 1.
Hot water temperatures required for automatic dishwasher
and laundry use can cause scald burns resulting in serious
personal injury and/or death. The temperature at which injury
occurs varies with the person’s age and time of exposure. The
slower response time of children, aged or disabled persons
increases the hazards to them. Never allow small children to
use a hot water tap, or to draw their own bath water. Never leave
a child or disabled person unattended in a bathtub or shower.

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sequences and safety features associated with a gas ignition
control system. The system continuously performs various
diagnostic tests to verify proper appliance and control
operation. Should an unsafe condition occur, the control
will shut down the burner and display a red service light as
well as indicate the cause of the error on the display. The
operating programs for the system are stored in permanent
memory inside the microcontrollers. User-selectable operating
parameters and a history of detected faults are stored in
rewritable memory in the microcontrollers. A loss of power
does not affect either of the memories.
INPUTS TO MCB
TEMPERATURE SENSORS:
Temperature probes (MCB - outlet and either inlet or tank are
required): The MCB accepts analog temperature inputs from
up to three sensors (inlet, outlet, and remote).
ECO input (MCB - required): The ECO (energy cut off) is a hi-
limit switch located inside the outlet probe. It is a normally
closed switch that opens if the probe is exposed to a
temperature higher than the trip point. Once tripped, the control
system needs to be manually reset.
Thermostat input (MCB - optional): This input is set up to work with
an externally connected thermostat that provides a contact closure.
If this input is closed and everything else is in the proper state, a “call
for heat” condition will be initiated. These leads should be shorted
together when a thermostat is not being used. If it is desired that the
thermostat control the temperature of the boiler, the operating setpoint
of the system should be set higher than the temperature that the
thermostat is controlling. This will allow the thermostat to control the
boiler. When the thermostat closes, a call for heat will be generated
until the thermostat determines that the required temperature has
been reached.
AIR PRESSURE SENSORS (OPEN CONDITION INDICATES FAULT):
Blocked Flue (MCB - required): Normally closed switch that opens
iftheuebecomesblockedduringoperation.
Blower Prover (MCB - required): Normally open switch that closes
when the air pressure produced by the blower is above the set point.
GAS PRESSURE SENSORS (OPEN CONDITION INDICATES FAULT):
Low Gas (MCB - required): Normally closed switch that opens when
the gas pressure falls below the trip level. This input is enabled/
disabled by a dip switch on the MCB
Hi Gas (MCB - required): Normally closed switch that opens if the
gas pressure exceeds a set value. This input is enabled/disabled
by a dip switch on the MCB.
WATER LEVEL SENSOR (OPEN CONDITION INDICATES FAULT):
Low Water Cut Off (MCB - optional): Normally open switch that
closes when water reaches preset level. This input is enabled/
disabled by a dip switch on the MCB.
WATER FLOW SENSOR:
Flow (MCB - required): Normally open switch that closes when
owexceedsasetvalue.
FLAME SENSOR:
Flame (MCB - required): Returns a signal to the microprocessor
ifameis detectedontheburner.Ifthe amerodismissingor
shorted,theamewillnotbedetected.
OUTPUTS FROM MCB
RELAY CONTACT OUTPUT:
Alarm (MCB - 24VAC - optional): Provides electrical power to
operate an external alarm. This can be an audio device (i.e.,
Sonalert), a visual device (lamp), or any other device that will
operate with the voltage and current level provided.
Pump (MCB - 120VAC - required on systems that do not have
an external pump): Provides electrical power to directly operate a
pump or the coil of an externally connected contactor.
Blower (MCB - 120VAC - required): Variable speed blowers utilize
the high blower output only.
Igniter (MCB - 120VAC - required): Provides power to operate
the HSI igniters.
Gas Valve (MCB - 24VAC - required): Provides power to activate
the gas valve. The gas valve cannot be activated when the ECO
contacts are open.
Low Water Cut Off (MCB - 24VAC - optional): Directly connected to
the 24VAC line to provide power to operate an external LWCO device.
MCB AND PDB INDICATOR LAMPS AND FUSES
A green LED is mounted on the PDB to indicate when line voltage
is applied (the PDB also contains a yellow and red LED, and a test/
run jumper that are used during installation to verify proper power
connections). A red LED on the MCB is used to indicate when the
24VAC input fuse has blown.
Yellow LEDs are located near the microcontrollers on the MCB.
These LEDs are “heartbeat indicators,” and blink approximately
twice per second to indicate that the microcontrollers are running.
MCB JUMPERS
The MCB has two jumpers. JP1 on the MCB is used to terminate
the external communications line. It is normally left off and installed
when the external cable is very long.
IGNITERS
The EMC modulation system operates with Silicon Carbide Igniters.
OPERATING SEQUENCE
1. The EMC modulation controller has four modes of operation:
Initialization, Standby, Running/Modulation, and Service. The
internal MCB micros control these modes through a sequence
of steps (or States) which are further described in the “UIM
Operating Procedures” section.
2. When power is applied to the system, it enters the initialization
mode and the following automatic functions are performed:
 • A.O.Smithopeningscreenisdisplayed.
 • The system goes through a calibration indicated by the
green running LED blinking and then staying on; next the
red service LED and yellow standby LEDs come on, next
the service and runnings LEDs blink ON and OFF.
 • Storedvaluesarerecalledfrommemory.
 • Congurationdipswitchesareread.
 • Pendingfaultsarerecalled
 • Microsonallboardsstartrunning(indicatedbyaashing
Yellow LED near each micro)
 • Inputsensorsareread
3. After initialization is complete (approximately 10 seconds)
the system turns the green LED off and goes to the standby
mode (yellow “Standby” LED on), unless a previously stored
fault has been recalled, which will send the system into the
service model (red “Service” LED on). In standby mode the
display shows the temperature screen and in fault mode the
current error screen is displayed.
4. The system then compares the temperature read from the
controlling probe (inlet or tank) to the setpoint temperature. If

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the temperature is less than the operating setpoint minus the
differential temperature and the thermostat input is closed then
a call for heat is established and the system shifts to the run
mode (green “Running” LED turns on).
5. The heating sequence begins by applying power to the pump.
6. After a few seconds the blower is turned on for 30-second
pre-purge period of combustion chamber.
7. The igniter is turned on.
8. After the igniter has reached a minimum of 2.8 amps, the gas
valveisenergizedtoallowgasowtoburner.
9. After an additional one second, the system checks the status
oftheamethroughtheamerod(sensor).Iftheameisnot
veriedwithin4seconds,thegasvalveisimmediatelyshut
off followed by 15-second inter-purge period, then the system
returns to step 7, if the “Trial for Ignition” dipswitch is set for
three (3) tries. If the dipswitch is set for one (1) trial, the system
will declare an error and boiler will require resetting the control.
10. Theboilerwillremainrunninguntilthesetpointissatised.
Once satised, the blower will continue for 15-second post
purge period.
11. Oncesetpointhashavebeensatised,theboilerpumpwill
continue to run for the programmed post-circulate cycle.
12. The control now enters the idle state as displayed by the
“Standby” LED. The control will continue to monitor heat
demand and state of other system devices. Upon a drop of
water temperature below the set parameters, the control will
return to step 5 and repeat the entire operating cycle. Note:
Any fault detection, during standby or running modes, will halt
the heating sequence and shift the system to the service mode
where the detected fault will be displayed.
NOTE: In standby and running modes the system constantly
monitors the signals and the internal operation for faults. Any
detected fault will halt the heating sequence and shift the system
to the service mode, where the detected fault will be displayed.
TEMPERATURE SETPOINTS (SYSTEM CONTROL ALGORITHM)
The boiler has a hysteresis type control, which means that it will
begin heating the water when the temperature sensed by the
control probe (inlet or tank) falls below the operating setpoint minus
the differential setpoint. It will stop heating the water when the
temperature rises to the operating setpoint.
UIM OPERATING PROCEDURES
FIGURE 2. - UIM, USER INTERFACE MODULE
The UIM receives commands from the user and displays operational
information to the user via an LCD (liquid crystal display) up to eleven
LED’s,andvetouchswitches.TheLCDprovidesinformationto
the user by the use of 10 menu-activated screens. Within each of
the screens, helpful information can be displayed by pressing the
“Help” button. The LED’s visually inform the user about the mode
the system is in. The touch switches allow the user to control the
operation of the system. The operation of these parts is described
in the following section:
UIM Screens:
On all screens a double vertical bar appears on the right side of
the display each time a key is touched to indicate that a key has
been activated. On several screens an indicator “>” appears on
the left side of the display to indicate the active line. The “Up/
Down” keys are used to move the indicator to the desired line and
the “Select” key is pressed to select the line. Also, on most of the
screens, up/down arrows appear on the right side of the screen
to indicate that there is additional lines either above or below the
displayed four lines.
• Menu Screen:
Displayed when the user presses the “Menu” key. This screen
is the selection point for the other 9 screens.
• Temperature Screen:
Displays the sensed temperatures of the Outlet, Inlet, and
Tank probes. Also displayed is the calculated Delta T (Outlet
minus Inlet) for the system. Shorted (“Short”) and disconnected
(“----”) probes are also displayed.
• System Status Screen:
This screen is used to view the status of switch inputs and output
states. An asterisk (*) is displayed next to the label when the
status is “True” (the description is fullled).  For example, if
waterisowing,ordetectedbytheowsensor,thenan“*”will
appear in front of the Flow label (i.e. *Flow). Another example
would be the ECO switch. If the outlet temperature is too high
the display will show: *ECO.
The System monitors the inputs at these times:
• ECO,BlockedFlue,LowGas,HiLimit,andHiGas-atalltimes
for a fault condition.
• Tstat-atalltimesforopen/closedconditions.
• Flow - for an on condition when the pump is on (no check for off
state)
• BlowerProver-whentheBlowerison.
• IgniterCurrent-foranonconditionapproximately18seconds
after the Igniter is turned on until the igniter is turned off and an
off condition at all other times.
• Flame-foranonconditionapproximately5secondsafterthe
gas valve is turned on until the valve is turned off and at all other
times for an off condition.
Control Status Screen:
Displays the status that the MCB micros are in. The MCB has
5 possible states and the FCB have 9. The normal MCB states
sequence is to move from Idle to Pre-Circulate when a call for
heatisinitiated.OnceheathasbeensatisedortheThermostat
is opened, the sequence moves to Post-Circulate and then back to
Idle. If a fault occurs at any time, the process jumps out of sequence
and goes directly to the appropriate Hard or Soft Fault state.
Description of MCB control states:
• Idle:
The yellow “Standby” LED is turned on and the system

13
waits for a heat request (determined by the Thermostat or
controlling probe inputs). All outputs are off in this state
except that if the Post-Circulate time is set to continuous,
the pump will be on. When the heat request is received,
the system moves to the Pre-Circulate state.
• Pre-Circulate:
The yellow LED is turned off and the green “Running” LED is
turned on. The green LED will remain on for all other states
except the fault states. Cold purging clears out any combustion
gas that may be in the combustion chamber. When purging is
complete the system moves to the Heat State.
• HeatStage
The system will command the FCB micros to start their heat
sequence. will be activated in order based on an algorithm
that determines how much heat is needed. The system will
remain in this state until the heat request is satisfied, the
Tstat is opened, or a fault occurs.
• SoftFaultState:(See“FaultDescription”sectionforlistof
soft and Auto Reset faults.)
The pump remains on for the selected post-circulate
time to cycle the hot water out of the boiler. The FCB is
commanded to shut down and the Alarm output is turned
on. The green LED turns off and the red “Service” turns
on. The MCB remains in this state until one of the following
occurs:
 • Onehourpasses(automaticrestartafteronehour)
 • IfCommunicationserrorsystemwillautomatically 
restart if communications re-establishes.
 • IfuserpressesSelectkeywhilecurrenterrorscreenis
displayed (Hard reset).
 • Ifhigh-limiterror-theoutlettemperaturedropsbelow
the high limit trip point minus the high limit differential.
(outlet water temperature drops to safe level). The fault
is logged in the error history when the fault state is
exited.
 • HardFault State:(See “FaultDescription” sectionfor
list of soft and Auto Reset faults.) The pump remains
on for the selected post-circulate time to cycle the hot
water out of the boiler. The FCB is commanded to shut
down and the Alarm output is turned on. The green
LED turns off and the red “Service” turns on and off
(flashes). The only way to exit this state is for the user
to press the Select key while the current error screen is
displayed. The fault is logged in the error history when
the fault state is exited.
While the MCB is in the Heating mode the FCB moves from
Idle, to Pre-Purge, to Heat Igniter, to Check for Flame, and
then to Heating. The process waits in this state until the call
for heat is satisfied, the thermostat input is opened, or a fault
occurs. When heat is satisfied, the sequence continues to
Post-Purge and then back to Idle. If three tries for ignition has
been selected on the MCB dipswitch and flame is not detected
at the appropriate time, then the sequence moves to the Inter-
Purge state for 15 seconds and the FCB heat sequence is
repeated. If flame is still not detected after the third try the
process declares a fault, jumps out of sequence and goes to
the error state. Other types of faults detected at any time will
also cause a jump to the error state.
Description of FCB control states:
• IdleState:
When any error is declared during idle state-The system will
remain in this state until the MCB request a heating cycle,
or a cold purge.
• Pre-PurgeState:
The blower is turned on. After 10 to 34 seconds (34
seconds for cold purging) the system switches to the Heat
Igniter State.
• HeatIgniterState:
The sequence of operation is as follows: “The igniter relay is
energized and the heat up period begins. After 18-20 seconds,
if the igniter has reached a minimum of 2.8 amps, the gas valve
safety circuit is then activated. If in this amount of time, the igniter
fails to reach a minimum amp draw of 2.8 amps, the unit will
re-cycle up to 3 times before locking out on igniter hardware
failure. If the igniter does reach the minimum required amp draw
of 2.8 amps, the gas valve circuit is energized, and the system
advances to Flame Check status.
• CheckforFlameState:
The gas valve is turned on. After 1.5 seconds, the system
checks that the gas valve relay is on. If it is not, the ignition
trial is considered to have failed and the system advances to
the Inter-Purge state, if any ignition trials remain, otherwise an
error is declared.
 Theamesensorischecked.Ifameisdetected,theigniter
is turned off. The state machine then advances to the Heating
State.Ifafter5seconds,theameisstillnotsensedthenthe
ignition trial is considered to have failed. The state machine
advances to Inter-Purge if any ignition trials remain, otherwise
an error is declared.
• HeatingState:
The system remains in this state until the call for heat is
cancelled or a fault occurs. The system returns to the Idle state
ifthecallforheatiscancelled,orsatisedandtotheappropriate
fault state if a fault occurs.
• Inter-PurgeState:
The gas valve and the igniter are turned off. The blower is on.
After approximately 15 seconds the system goes back to the
Heating Igniter State.
• Post-PurgeState
The gas valve and the igniter are turned off. The blower
is then left on for approximately 25 seconds, the system
returns to the Idle state.
• ErrorState
The gas valve and the igniter are turned off. The FCB micro tells
the MCB micro which error has occurred. The system waits in
this state until the MCB sends a command to clear the error,
and the system returns to the idle state.
• ColdPurgeState
Cold purge occurs when the MCB micro commands the blower
to go on before lighting to clear the unit of residual gases.
This state normally lasts approximately 32 seconds but on a
specialsituationcanlastupto5minutes.Ifontherstcallfor
heat after power up, blower prover switch is open, this state
will take up to 5 minutes before declaring an error.
The MCB will wait the normal cold purge time (normally 32
seconds) before checking for activation of all active blower
prover. If blower prover is active at this time the MCB cancels
thecoldpurgerequest.Aftertherstcoldpurgehasbeendone
aagissettopreventfurtheractivationoftheshutteradjust5
minute delay. Any further requests for cold purge will last the
normal cold purge time. The FCB will go into fault mode if the

14
blower prover does not activate after 15 seconds. This time
allows the blower relay to activate, the blower to come up to
speed,andtheresponsefromtheblowerprovertobeltered.
• UserSettingsScreen:
Each setpoint or user setting has either a limited selection of
values, or a limited range of values. The Up/Down keys are
used to change values. After changing an item, the Select key
is pressed to accept the change, or the Menu key is pressed
to reject the change and restore the item to its original value.
The following setpoints can be changed:
• OperatingSetpoint:
This setpoint sets the base temperature for the control algorithm.
OPERATING SETPOINT ADJUSTMENT PROCEDURE
The system has a standard programmable Operating Setpoint
range of 70°F (21°C) to 190°F (88°C) for a VW and of 70°F
(21°C) to 220°F (104°C) for a VB for either a Remote or inlet
probe depending on selection. The user can easily change
the Operating Setpoint at any time by using the following
procedure. When any configuration or setpoint is changed
(and the Select key touched), the new value is IMMEDIATELY
saved to non-volatile memory. The factory default setting is
145°F (49°C).
1. Press the MENU key.
2. Scroll the “>” with the DOWN key next to the USER SETTING
SCREEN.
3. Press the SELECT key.
4. Scroll the “>” with the DOWN key until it is pointing to
OPERATING SETPOINT.
5. Press the SELECT key.
6. Use the UP or DOWN key to select the value you wish to enter.
7. Press the SELECT key to accept and store the new value.
• HighLimit:
The outlet temperature probe contains both an ECO switch
and a thermistor for temperature measurement. The sensed
outlet temperature is used for the automatically resettable High
Limit setpoint. If the sensed outlet temperature exceeds the
High Limit setpoint, a “soft lockout” condition will occur and
the burner will be shut off. This fault condition is automatically
cleared when the temperature drops below the high limit
setpoint minus the high limit differential.
AUTO HIGH LIMIT SETPOINT ADJUSTMENT PROCEDURE/
OUTLET TEMPERATURE PROBE
The High Limit setpoint has a range of 90°F (32°C) to 210°F (99°C)
for a VW and a range of 90°F (32°C) to 235°F (113°C) for a VB.
Use the following procedure to change the automatically resettable
High Limit Setpoint:
1. Press the MENU key.
2. Scroll the “>” with the DOWN key next to USER SETTING SCREEN.
3. Press the SELECT key.
4. Scroll the “>” with the DOWN key until it is pointing to HIGH
LIMIT SETPOINT.
5. Press the SELECT KEY.
6. Use the UP and DOWN key to select the value you wish to enter.
7. Press the SELECT key to accept and store the new value.
• HighLimitDifferential:
The outlet temperature must be below the automatic High Limit
setpoint minus the High Limit Differential setpoint before a call
for heat can be generated.
HIGH LIMIT DIFFERENTIAL SETPOINT ADJUSTMENT
PROCEDURE
The High Limit Differential Setpoint has a range of 1°F to 50°F for
all models. Use the following procedure to change the High Limit
Differential Setpoint:
1. Press the MENU key.
2. Scroll the “>” with the down key next to USER SETTING
SCREEN.
3. Press the SELECT key.
4. Scroll the “>” with the DOWN key until it is pointing to HIGH
LIMIT DIFFERENTIAL SETPOINT.
5. Press the SELECT key.
6. Use the UP or DOWN key to select the value you wish to enter.
7. Press the SELECT key to accept and store the new value.
• Operating Differential Setpoints:
Each of the two stages has an independent Operating
Differential setpoint.
• Temperature Units:
Temperature can be displayed in either °F or °C units.
• Post Circulate Delay Time:
The time circulation pump will stay on after the burner
is turned off. The time in seconds is adjustable with
the following values: 45, 90, 180 or continuous. If the
continuous value is selected the pump will remain on at
all times and the post circulate state time will be set at
45 seconds.
• Network Address:
This is a unique number assigned to this boiler to differentiate
it from other boilers or water heater on the same A. O.
Smith proprietary network. A valid Network Address can be
any number from 0 to 31. It is set by default to zero, which
is an invalid address. The boiler will not communicate until
it is changed to a valid and unique number. This prevents
two units from trying to respond to the same request from
the PC or supervisory network device.
• Configuration Settings Screen:
Displays the status of the dipswitches installed on all
boards as described earlier.
• Log & System Info Screen:
Displays the following information:
Elapsed hours of operation (Total time system has been
powered up)
Number of running minutes (Number of minutes system has
been in the run mode)

15
kBtu rating of the boiler (0 to 5750kBtu in 10kBtu increments)
The software revision level of the MCB.
•Current Error Screen:
Displays the last error that the system has detected plus
a time stamp of when the error occurred. (The time stamp
is based on the elapsed hours value at the time the error
occurred. It is displayed in hours and minutes. This error
remain displayed as long as it is still valid. When cleared
it is moved to the Error History Screen. The system will
automatically jump to this screen when an error is detected.
It will also go to this screen upon power-up if an error
was still valid when power was turned off.
NOTE: Errors are cleared from this screen by pressing
the “select” key.
• Error History Screen:
This screen displays a list of the last 9 errors (with time
stamps) that have occurred. The last error to occur is
displayed first.
• Reload Defaults Screen:
From this screen the user can restore the factory default
values for screen adjustable configurations by pressing
the Select key. The values restored are as follows:
VW Models
Oper Setpnt (Operating Setpoint) - 145° F (63° C)
Hi Limit (High Limit Setpoint) = 210° F (99° C)
Hi Limit Dif (High Limit Differential) = 20° F (11° C)
VB Models
Oper Setpnt (Operating Setpoint) = 190° F (88° C)
Hi Limit (High Limit Setpoint) = 230° F (110° C)
Hi Limit Dif (High Limit Differential) = 20° F (11° C)
Both Models
Tempert Units (Temperature Units) = F
Post Cir Secs (Post Circulation pump delay = 45 seconds
Network Address (Network Address) = (none)
UIM Touch Switches
BelowtheLCDdisplayarevetouchswitchesorkeys,thatthe
operator uses to operate the system.
• MenuKey:
Pressing this key activates the menu screen where the other
screens can be accessed.
• SelectKey:
This key performs several functions. Screens can be selected
from the menu screen by pressing this key when the “>” appears
next to the screen desired.
On the User Settings screen items that appear next to a “>”
symbolcanbeselectedwiththiskey.Ifasetpointconguration
itemisselected,the“>”willthenashslowlytoindicatethatthe
item has been selected. The Up and Down keys are then used
to change its value.
From the Current Error Screen this key is used to reset the
system from an error:
• Up and Down Keys:
These keys are used to move upwards and downwards in
screens to reach a desired item and to change setpoints
and user settings. They have an auto increment/decrement
feature for some of the configurations and values. When
you first press one of the keys and value changes by 1
count, then wait 1/2 second and changes slowly until the
key is released or if held for 3 or more seconds it will
change the value quickly.
• HelpKey:
Pressing the Help key from any screen displays helpful
information about that screen. From the menu screen,
general help information is displayed as to how to use the
user interface. To return to the previous screen press the
Help or Select keys, or press Menu key to go to the menu
screen. If a small down arrow appears in the lower right
hand corner then there is off screen content below what
is displayed. Press the down arrow to scroll down to this
information. After scrolling down an up arrow will appear in
the upper right hand corner to indicate off screen content
above what is displayed.
UIM LED’s
The three LED’s to the right of the LCD indicate the status
of the overall system. The red LED indicates that a fault has
been detected and the system has stopped running. It is on
continuously for soft faults and flashes for hard faults. The
Yellow LED indicates that the boiler is in a ready mode waiting
for a call for heat command. When on continuously the Green
LED indicates that the system is in the heating mode. If it is
flashing it indicates that the UIM is in the initialization mode
and the touch switches are being calibrated.
The VF boiler has a display on the UIM which is a scaled display
indicatingthecurrentringrateoftheboiler(25%to100%).
Fault Messages and Troubleshooting Guide
The EMC 5000 modulation system does excessive self-diagnostics
and displays detected faults on the UIM display in an easy to read
manner. There are approximately 80 different faults that can be
detected. Some of the faults are caused by internal problems and
some by external causes. The faults create different types of system
lockouts (shut down). Hard lockouts are serious problems that
require the user to manually restart the system. Soft lockouts can
be reset by the user or after 60 minutes the system will automatically
clear the error and restart. Auto Reset lockouts will monitor the
cause of the fault and it the fault clears itself the system resets
itself. The following table shows the fault messages and some
possible troubleshooting hints:

16
TROUBLESHOOTING IGNITION SYSTEM
Fault Messages and Lockout Status (* = stage number: 1, 2, 3, or 4)
FAULT DISPLAYED DESCRIPTION RED LED LOCKOUT
“Display Fail” Communications with UIM interrupted Continuous Auto Reset
Check communication cable to UIM. Try moving to other Internal Communications connector on MCB.
Also check the connectors where the cable is plugged in for best connecting wires.
“Comm. Fail Stg.*” Communications with FCB interrupted Continuous AutoReset
Same as above. Also try swapping FCB and UIM communications cables.
“Low AC Voltage” Line voltage less than 90 vac Continuous Auto Reset
Check incoming power line for loss of voltage. May also be caused by a power line brown-out (momentary loss of voltage)
“Low 24VAC” Voltage from transformer less than 18 vac Continuous Auto Reset
Check transformer output. Should be over 24vac. May be caused by excessive current drain or a faulty transformer
“Brown Out Reset” Indicates a brown out reset occurred - - - - None
Caused by a momentary dip in voltage on the MCB +5vdc power bus. Contact factory. (Not considered a serious
problem if it only occurs on very rare occasions.)
“Timeout Reset” Indicates a watchdog reset occurred - - - - None
Caused when the micro executes the software in an improper way. Contact factory. (Not considered a serious
problem if it only occurs on very rare occasions.)
“FCB Comm Timeout” FCB did not receive command from MCB Continuous SOFT
Caused when communications between the MCB and the FCB are interrupted. May occur when a surge of power on
a nearby device (i.e. arc welder) creates an EMI burst. Not a serious problem if it occurs rarely.
“No Flow” Water is not owing Continuous SOFT
Causedbytheowswitchbeingopenwhenitshouldbeclosed.Checkwaterlines,pump,owswitchcontacts,wiring.
“Blower Prov Stg* Blower pressure is too low it they should have been closed. Continuous SOFT
Check blower, switch contact, wiring, and for air leaks.
“Blocked Flue” Flue is Blocked Continuous SOFT
Causedbytheblockedueswitchcontactsbeingopenwhentheyshouldhavebeenclosed.Checkforueblockage,
switch contacts, wiring.
“Blocked Inlet” Air inlet is blocked
Checkinletterminal,venturiscreenandburnertubefordebris.Ifinletisclearcheckblockedinletueswitchforcontinuity.
Inspect hose to switch to ensure it is connected and not cracked or split.
“High Limit” Outlet temp. exceeded high limit setpoint Continuous Auto Reset
Caused when the temperature of the outlet probe exceeds the high limit setpoint. This is an internal “software” limit
switch and not an actual device. Check that the over temperature is not being caused by improper setup or
operation of the boiler.
“MRHL fault” Outlet temp is too high Flashing HARD
Caused when the MRHL (a thermostat) contacts in the Outlet probe are open when they should be closed. Fault may
be due to high outlet temperature, bad switch contacts in the Probe, or disconnected wiring. Note: The MRHL can be
checked by disconnecting the outlet probe from the MCB and reading the resistance across the two active pins on the
connector at the end of the probe cable. The value should be approximately 0 ohms when the temperature of the probe is less than 220°F.
“Low Water” Water level is too low Flashing HARD
Caused by the Low Water Cut Out device not closing its feedback switch contacts when it should. Check water line,
switch contacts, wiring, LWCO.
“Low Gas” Gas pressure is too low Flashing HARD
Caused by the Low Gas switch being open when it should be closed. Check gas line, switch contacts, wiring.
“Powered Accessory” Power vent not running Flashing HARD
Caused by the Powered Vent device not closing its feedback switch contacts when it should. Could also be caused
by a problem with the relay output on the MCB. Check output to powered vent, switch contacts, wiring.
“High Gas Stg*” Gas pressure too high Flashing HARD
Caused by the High Gas switch being open when it should be closed. Check gas line, switch contacts, wiring.
“Inlet Probe” Inlet probe shorted or open Flashing HARD
Caused when the thermistor in the probe or the wiring to the probe is shorted or disconnected. Check the probe.
Note: The thermistor and wiring can be checked by disconnecting the probe from the MCB and reading the resistance
across the two active pins on the connector at the end of the probe cable. The value should be approximately 10K
ohms (value will change slightly with changes in temperature).
“Outlet Probe:” Outlet probe shorted or open Flashing HARD
Caused when the thermistor in the probe or the wiring is shorted or disconnected. Check the probe. Note: the
thermistor and wiring can be checked by disconnecting the probe from the MCB and reading the resistance across
the two active pins on the connector at the end of the probe cable. The value should be approximately 10K ohms
(value will change slightly with changes in temperature).
“Tank Probe” Tank (Remote) probe shorted or open Flashing HARD
Caused when the thermistor in the probe or the wiring is shorted or disconnected. Check the probe. Note: the
thermistor and wiring can be checked by disconnecting the probe from the MCB and reading the resistance across
the two active pins on the connector at the end of the probe cable. The value should be approximately 10K ohms|
(value will change slightly with changes in temperature).
“Igniter Stg*” Igniter current is too low Flashing HARD
Caused by a low current draw problem with the igniter. This may occur if the igniter is old, damaged, or disconnected
and no longer draws the proper level of current. This condition will affect the ability of the igniterto get hot enough to
 rethegasproperly.Checktheigniteranditsassociatedwiring.
“Igniter Pwr Stg*” Improper power applied to the igniter circuit Flashing HARD
Caused by improper line power being applied to the igniter circuitry. Check line connections. Paying particular attention to
the earth ground connection. Also check that line voltage does not exceed 132 VAC RMS.
“Igniter Hdwr Stg*” Hardware problems with igniter circuit Flashing HARD

17
Thisisapre-mixburnersystem.Theameisnotsupposedtobe
directlyontheburner.Theameshouldbejustabovetheburner
deck approximately 1/8” and blue in color, see illustration.
FIGURE 3. - BURNER FLAMES
Visually check flame characteristics through the view port
located on the top head of the boiler. The “Burner Flames”
illustration shows the normal flame condition.
These boilers are designed to give many years of efficient and
satisfactory service when properly operated and maintained.
To assure continued good performance, the following
recommendations are made.
The area around the unit should be kept clean and free from
lint and debris. Sweeping the floor around the boiler should
be done carefully. This will reduce the dust and dirt which
may enter the burner and heat exchanger, causing improper
combustion and sooting.
MAIN BURNER
Check main burner every three months for proper flame
characteristics. The main burner should display the following
characteristics:
• Providecompletecombustionofgas.
• Causerapidignitionandcarryoverofameacrossentireburner.
• Givereasonablyquietoperationduringinitialignition,operation
and extinction.
•Causenoexcessiveliftingofflamefromburnerports.
If the preceding burner characteristics are not evident, check for
accumulation of lint or other foreign material that restricts or blocks
the air openings to the burner or boiler. To check burners:
1. Shut off all gas and electricity to unit. Allow unit to cool.
2. Remove main burner from unit.
3. Check that burner ports are free of foreign matter.
4. Clean burner with vacuum cleaner. DO NOT distort burner ports.
5. Reinstall burner in unit. Ensure that all the screws on the burner
angearetightenedsecurelysothatthegasketwillprovidea
good seal.
6. Also check for good flow of combustion and ventilating air
to the unit.
After placing the boiler in operation, check the ignition system
safety shut-off devices for proper operation. To accomplish this
with the main burner operating, close the valve on the manifold.
Within four seconds the main burner should extinguish. If this
does not occur immediately, discontinue gas supply by closing
main manual shut-off and call a qualified service agent to
correct the situation. If the burners extinguish, then light boiler
in accordance with lighting and operating instructions.
PREVENTATIVE MAINTENANCE

18
Any safety devices including low water cutoffs used in conjunction
with this boiler should receive periodic (every six months) inspection
toassureproperoperation.Alowwatercutoffdeviceoftheoat
typeshouldbeushedeverysixmonths.Periodicchecks,atleast
twice a year, should be made for water leaks.
More frequent inspections may be necessary depending on water
conditions.
The boiler-mounted gas and electrical controls have been designed
to give both dependable service and long life. However, malfunction
can occur, as with any piece of equipment. It is therefore
recommended that all components be checked periodically by a
qualiedserviceagentforproperoperation.
RELIEF VALVE
Burn hazard.
Hot water discharge.
Keep clear of Pressure
Relief Valve discharge outlet.
The pressure relief valve must be manually operated at least
once a year. Caution should be taken to ensure that (1) no one
is in front of or around the outlet of the pressure relief valve
discharge line, and (2) the water manually discharged will not
cause any bodily injury or property damage because the water
may be extremely hot.
To test the relief valve, lift the lever at the end of the valve several
times, see Figure below. The valve should seat properly and
operate freely.
DISCHARGE
PIPE
RELIEF VALVE
FIGURE 4. - RELIEF VALVE
If after manually operating the valve, it fails to completely reset
and continues to release water, turn off power to the boiler at the
main disconnect switch or breaker. Close the cold water inlet to the
boiler and follow the draining instructions in this manual to drain
the boiler. Should the relief valve need to be replaced, call the toll
free phone number listed on the back of this manual for further
technical assistance.
COMBUSTION AIR FILTER
If the combustion air supply to the boiler contains dust, dirt, drywall
dustetc.altermustbeinstalled.Anairlterisnotsuppliedwith
the boiler as shipped from the factory. The installer must provide a
lteringsystemintheairinlettotheboilerifdust,dirtorconstruction
dirt can be pulled into the boiler through the inlet air piping.
Periodicallycleanairlterperthemanufacturer’sinstructions.
BLOWER COMPARTMENT
The blower compartment should be cleaned annually to remove any
dirt and lint that may have accumulated in the compartment or on the
blower and motor. Buildups of dirt and lint on the blower and motor
can create excessive loads on the motor resulting in higher that
normal operating temperatures and possible shortened service life.
BURNER MAINTENANCE
Qualiedservicersshouldfollowthisprocedurewhentheboiler’s
burner needs cleaning.
1. Turn off the electrical power to the boiler and close the main
manual gas shutoff valve(s). Allow the boiler parts to cool before
disassembly.
2. Loosentheangeandseparatethegastrainfromthemanifold
assembly.
3. Separatetheburnerfromthebloweradapterbyrstremoving
the four (4) bolts and subsequently, the blower gaskets. The
blower should be free to move at this point.
FOR DIRECT VENT UNITS: It is necessary to loosen and slide the
rubber coupling on the blower adaptor in order to move the blower.
4. Loosen the seven bolts on the blower adapter at the base and
move the burner ground wire (Green) aside.
5. Lift the blower adapter and remove the manifold assembly up
from the 6 studs located on the cover plate and remove the
burner gasket.
6. Remove any loose foreign material such as dust or lint with a
vacuum. Check all ports for blockage. Dislodge any foreign
material causing blockage. Remove any soot or carbon deposits
with a rag making sure to remove any lint left on the burner by
vacuuming again.
7. Reverse the steps to reassemble the unit.
8. Restore electrical power and gas supply to the boiler.
• Put the boiler back in operation by following the Lighting and
Operating instructions in this manual.
• Check for gas leaks and proper boiler and vent operation.
CONDENSATE REMOVAL SYSTEM
Due to the highly efcient operation of this unit, condensate is
formed during operation and must be removed by the condensate
drain systems. Inspect the condensate drains and tubes at least
onceamonthandinsuretheywillallowthefreeowofcondensate
at all times. The system must be inspected more frequently in
cold weather if the drain system is located in an area, such as
alongthe oor,wherefreezingtemperaturesarelikelyto occur.
The condensate drain system must be protected against freezing.
Contactaqualiedserviceagenttoinspectandcorrectthecondition
if freezing of the condensate lines is a problem. The unit is equipped
withablockedueswitchwhichwillshuttheunitoffifcondensate
isunabletodrainandbacksupintheunit.Ablockedueerrorwill
appearwhensufcientcondensateaccumulatesforthiscondition.
The transparent drain lines and condensate drain on the bottom
of the vent collector should be visually inspected at one month
intervals for blockage, particularly in the areas of the loops in the
lines which trap a small amount of condensate, and the exit point
of the vent collector drain. Condensate in portions of the line other
than the loop area indicates a blockage in the drain line. Flush the

19
lines with air or water and clear or replace the blocked portions
of the line as necessary. Note that areas of the drain line which
include a sag or low spot in the line will also form a condensate trap
which can be removed by levelling the tube and does not indicate
a blocked system.
Inspect the metal vent drain and vent collector drain connectors
at six month intervals. Remove the hoses from the connections,
then check with a small wooden dowel or plastic rod passed up
through the metal connection to insure the passage is clear,
using caution to not bend or damage the connector. Call a
qualiedserviceagenttoinspectandcorrecttheproblemifany
obstructions are found in the connectors. Replace all hoses and
clamps immediately after inspection and before starting the boiler
in accordance with the Lighting and Operating Instructions. DO
NOT OPERATE THE BOILER UNLESS ALL CONDENSATE
DRAIN LINES ARE PROPERLY CONNECTED AND WORKING.
When a means to neutralize condensate has been installed
you must also follow operating, inspection and maintenance
proceduresspeciedbythemanufactureroftheproduct.Inspect
the installed device to insure that it does not cause condensate
to remain in the boiler or vent for any reason.
VENTING MAINTENANCE
It is recommended that the intake and exhaust piping of the
appliance be checked every 6 months for dust, condensate leakage,
deterioration and carbon deposits.
Qualied service agent should follow this procedure when the
boiler’s intake and exhaust piping need cleaning:
1. Turn off the electrical power, and manual gas shut-off.
 • Allow boiler parts to cool before disassembly.
2. Remove the vent pipe.
•Check parts and chimney for obstructions and clean as
necessary.
3. Remove burner from boiler and other metal parts as required
to clean as necessary.
•Refer to parts list for disassembly aid.
4. Clean and reinstall the parts removed in steps 2 and 3.
•Be sure the vent pipe has a minimum upward pitch of 1/4"
per foot (2cm/m) of length and is sealed as necessary.
5. Restore electrical power and gas supply to boiler.
•Check for gas leaks and proper boiler and vent operation.
HEAT EXCHANGER PREVENTIVE
MAINTENANCE
In most water supply systems solids exist.As the water is heated, these
tend to drop out depositing as scale or lime. This scale must be removed
before the heat exchanger tubes become blocked.
DELIMING
The amount of calcium carbonate (lime) released from water is
in direct proportion to water temperature and usage. The higher
the water temperature or water usage, the more lime deposits are
dropped out of the water. This is the lime scale which forms in
pipes, boilers and on cooking utensils.
The usage of water softening equipment greatly reduces the
hardness of water. However, this equipment does not always
remove all of the hardness (lime). For this reason it is recommended
that a regular schedule for deliming be maintained.
The time between cleaning will vary from two to six months
depending upon water conditions and usage. A change
of approximately 5°F (3°C) in the normal temperature rise
through the boiler is usually an indication that scale should
be removed. For long life, copper or brass is recommended
for all valves, pipe and fittings.
TUBE CLEANING PROCEDURE
MECHANICAL REMOVAL OF DEPOSITS
Establish a regular inspection schedule, the frequency depends
on the local water conditions and severity of service. Do not let
the tubes clog up solidly. Clean out deposits over 1/16” (1.6mm)
thickness.
To service heat exchanger tubes, remove return header casting on
the side opposite the water connections. Use a U.S. standard 5/8”
deep socket ratchet to remove the nuts, exposing the tube ends.
Inspect to ensure tubes are free of scale and deposits. If scaled,
remove deposits with a stiff wire brush or mechanical tube cleaner
to bare metal. Reinstall return header casting. Flush system.
Note: Removal of the heat exchanger is not required.
REPLACEMENT PARTS
Replacement parts may be ordered through A. O. Smith dealers,
authorized servicers or distributors. Refer to the Yellow Pages for
where to call or contact (in United States) the A. O. Smith Water
Products Company, 500 Tennessee Waltz Parkway, Ashland
City, TN 37015, 1-800-433-2545 or (in Canada) A. O. Smith
Enterprises Ltd., 768 Erie Street, Stratford, Ontario, Canada
N5A 6T3, 519-271-5800. When ordering parts be sure to state
the quantity, part number and description of the item including the
complete model and serial number as it appears on the product.
Refer to the parts list (P/N 212802-002) for more information.
For Technical Assistance call A. O. Smith Technical Information
Center at 1-800-527-1953.

20
NOTES