A.O. Smith VF VB 1000 How to use

Variable Fire Boiler
Domestic Hot Water/Hydronic Heating
VF Boiler
MODELS COVERED
VW and VB 500, 750, and 1000 Models
Series 100 and 101
Part No. TC-099
Service Handbook
Part No. TC-099 • Printed in the U.S.A. • 0407
©2007 A. O. Smith Corporation
COMMERCIAL
Visit the “Information Central” link of
www.hotwater.com for a listing of
available Service Handbooks.
For additional information contact:
A. O. Smith Water Products Company
A Division of A. O. Smith Corporation
500 Tennessee Waltz Parkway
Ashland City, TN 37015
1-800-527-1953
www.hotwater.com

A. O. SMITH WATER PRODUCTS COMPANY
VF BOILER SERVICE MANUAL
Technical Training Department ©2007
CONTENTS
Introduction.......................................................................
Qualifications....................................................................
Service Warning................................................................
Tools Required..................................................................
EMC 5000 Modulation Control System...........................
UIM - User Interface Module - Overview..........................
UIM - Status Lights............................................................
UIM - Input Buttons...........................................................
UIM - Changing Settings..................................................
UIM - Menu Screens..........................................................
Principles of Operation....................................................
VFD and Blower Operation..............................................
Venturi Operation - Gas Train..........................................
Blower Speed Verification - Hall Effect Sensor..............
Config Key - Blower Speed Programming......................
Sequence Of Operation....................................................
START UP PROCEDURE..................................................
Adjusting Manifold Gas....................................................
Poor Combustion - Ignition Problems............................
Manifold Gas Pressure Check.........................................
Control Panel Layout........................................................
MCB - Modulation Control Board....................................
PDB - Power Distribution Board......................................
2
2
2
3
4
4
6
7
8
9
11
11
12
13
14
15
17
19
20
23
24
25
35
Troubleshooting - Error Messages..................................
Display Is Blank................................................................
Error Message “Display Fail”..........................................
Error Message “No Config Key”......................................
Error Message “Config Key CRC”...................................
Error Message “Config Key Part”....................................
Error Message “Low AC Voltage”....................................
Error Message “Low 24 VAC”..........................................
Error Message “Low Water”............................................
Error Message “Low Gas”...............................................
Error Message “No Flow”................................................
Error Message “Sequence Err”.......................................
Error Message “Ignition Speed”......................................
Error Message “Mtr Spd < Min Spd”................................
Error Message “Blower Prov Stg1”.................................
Error Message “Blocked Flue”........................................
Error Message “Flame Stg1.............................................
Error Message “Igniter Stg1.............................................
Boiler Controls Information.............................................
Operating Temperatures..................................................
Bypass Lines.....................................................................
Technical Specifications..................................................
Glossary............................................................................
41
42
43
43
44
44
45
45
45
45
46
48
48
48
49
56
57
60
61
67
67
68
71

VF BOILER SERVICE MANUAL
AOS WPC - Tech Training 2 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
INTRODUCTION
This Service Manual is designed to aid in servicing and troubleshooting A. O. Smith VF
boilers. Models VW/VB 500 - 1000 - series 100/101 boilers are covered in this manual.
The instructions and illustrations contained in this service manual will provide you with
troubleshooting procedures to verify proper operation and diagnose and repair common
service problems.
Important Service Reminder
When performing any troubleshooting step outlined in this service manual always consider
the wiring and connectors between components. Perform a close visual inspection of all
wiring and connectors to and from a given component before replacement. Ensure wires
were stripped before being crimped in a wire connector, ensure wires are crimped tightly in
their connectors, ensure connection pins in sockets and plugs are not damaged or worn,
ensure plugs and sockets are mating properly and providing good contact.
Failure to perform this critical step or failing to perform this step thoroughly often results in
needless down time, unnecessary parts replacement, and customer dissatisfaction.
Instruction Manual
Have a copy of the Instruction Manual that came with the boiler on hand for the model and
series number before servicing.
Installation information given in this service manual is not a complete installation instruction.
Installation information covered in this service manual has a limited focus as it applies to
servicing the boiler. This Service Manual does not replace or supersede the Instruction
Manual that came with the boiler. Always refer to the Instruction Manual that came with the
boiler for complete installation instructions.
Qualifications
Service of A. O. Smith VF boilers requires ability equivalent to that of a Qualified Service
Agent (defined by ANSI below) in the field involved. Installation skills such as plumbing, air
supply, venting, gas supply, electrical supply are required in addition to electrical testing
skills. Start up and servicing of VF boilers requires combustion analysis test equipment.
ANSI Z223.1 2006 Sec. 3.3.83: “Qualified Agency” - “Any individual, firm, corporation or
company that either in person or through a representative is engaged in and is responsible
for (a) the installation, testing or replacement of gas piping or (b) the connection, installation,
testing, repair or servicing of appliances and equipment; that is experienced in such work;
that is familiar with all precautions required; and that has complied with all the requirements
of the authority having jurisdiction.”
Service Warning
If you are not licensed or certified to perform a given task do not attempt to perform any of
the service or installation procedures outlined in this manual. If you do not understand the
instructions given in this manual or do not feel confident in your abilities to perform a given
task do not attempt to perform any procedures outlined in this manual.

AOS WPC - Tech Training 3 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
VF BOILER SERVICE MANUAL
Tools Required
• Instruction Manual that came with the boiler.
• Hand tools common to installation and service of commercial water heaters and boilers.
• TORX® T40 or 5mm hex wrench - for setting gas mixture at gas valve.
• 3mm or 7/64in hex (allen) wrench - for setting gas mixture at gas valve.
• Two - U tube manometers (preferably) or gas pressure gauges. U tube manometers can
be used to accurately measure supply gas pressures. However, their resolution is
insufficient to be used for measuring draft, manifold gas pressure on VF boilers, or
perform air pressure switch testing. U tube manometers or gas pressure gauges may not
be substituted for Digital Manometers listed below.
• Digital Manometer (s) range -20.00 to +20.00" W.C., resolution 0.01" W.C. Recommend
UEI model EM200 or equivalent. Used to test performance of air pressure switches,
measure draft, and measure manifold gas pressure.
• True RMS Digital Multi Meter DMM, recommend UEI model DL289 or Fluke equivalent.
Capable of measuring:
AC/DC Voltage
VAC Frequency (Hz)
Ohms
DC micro amps µA
• AC amp meter- recommend UEI model DL289 or equivalent.
• Combustion analyzer
Capable of measuring:
CO2
CO
Draft Pressure
Exhaust Temperature
Efficiency

VF BOILER SERVICE MANUAL
AOS WPC - Tech Training 4 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
EMC 5000 MODULATION CONTROL SYSTEM
This portion of the service manual will cover the EMC 5000 Modulation Control system
(EMC - Energy Management Control). The EMC 5000 control system includes several
components: a UIM (User Interface Module), a MCB (Modulation Control Board), and a PDB
(Power Distribution Board). The EMC 5000 Control System can control single stage,
multiple stage, and modulating boilers and water heaters. This service manual should be
used as a reference for A. O. Smith VW/VB 500-1000 Series 100-101 boilers only.
Features Include:
•EMI / RFI filtering - built into all circuit boards. (EMI = Electro Magnetic Interference, RFI
= Radio Frequency Interference) Helps prevent or eliminate erratic operation caused by
EMI/RFI.
•Help screens - text based operational information to help the user understand how to
change settings and navigate the menu screens.
•Self diagnostics - text based diagnostic information (error and fault messages) on board
to help service technicians quickly and accurately service the boiler.
•Error message log - will retain a 9 event history (plus the current event) of error
messages with a time stamp. This will help diagnose load and/or environmental conditions
that may be contributing to a problem with operation or a lock-out.
•Short cycling protection - if any stage logs more than 30 cycles in one hour the control
enters a short cycle prevention condition. The boiler will continue to operate in this mode.
The UIM will display and log a “Short Cycle Cond” error message with the yellow Standby
system status LED flashing. The MCB will add a 180 second delay before activating any
stage’s call for heat after the last call for heat during this operating mode.
The short cycle protection mode can be ended (reset) by touching the Select button on the
UIM while the error message is displayed.
•Temperature probe filtering - The inlet, outlet, and remote Tank/Loop temperature
probes are read twice per second by the MCB and are filtered for 4 seconds. This filtering
will help prevent rapid short cycling caused by momentary fluctuations in temperature.
•Pressure/flow switch filtering - input switches such as air pressure switches are read
every second by the MCB and are filtered (de-bounced) for 6 seconds. This desensitizes
the input signal and will help prevent nuisance error/fault conditions due to momentary
fluctuations caused by wind gusts or blower speed changes. The flow switch is filtered for
4 seconds.
•Network capability - multiple boilers can be networked together (daisy chained) with
standard Category 5/6 network cable and given individual network addresses.
•Access/monitoring with future A. O. Smith EMS (Energy Management System)
controller.

AOS WPC - Tech Training 5 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
VF BOILER SERVICE MANUAL
UIM - USER INTERFACE MODULE - OVERVIEW
The UIM is an assembly that consists of several electronic components. The main circuit
board in the assembly is the UIB (User Interface Board) which houses the communications
port. The UIB relays user input and data to and from the MCB, controls the LCD, and
activates the LEDs. Mounted to the UIB is a TSB (Touch Sensor Board) containing the touch
sensor pads that are the user input buttons. There is a LCD module mounted to the UIB that
displays operational information and diagnostic messages in plain English.
LEDs
(Light Emitting Diode)
• Three “System Status” LED lights: Service, Standby, Running.
Located to the right of the LCD.
• Firing Rate Status indicator - located in the lower right portion of
the UIM. Four LED lights behind a green (gradient) translucent
cover. This display indicates the approximate firing rate
between 25% and 100%.
LCD
(Liquid Crystal Display)
• LCD display - 4 lines, up to 20 characters per line.
• 10 different screens - Menus, Temperatures, System Status,
Control States, User Settings, Configuration Settings, Log &
System Information, Current Error, Error History, and Reload
Defaults (see page 9).
• Text based operational and diagnostic information.
User Input Buttons • Select - Menu - Help - Up - Down.
• 5 touch sensitive buttons for user input. Located on the lower
left portion of the UIM.
• No moving parts - no pressure is required; these buttons
activate on finger presence.
Settings / Memory • Non volatile memory; once new settings are confirmed
(touching the Select button) they remain in memory.
LCD display
4 line x 20 character
Firing Rate Status
5 Touch Sensitive
User Input Buttons
System Status
LEDs

VF BOILER SERVICE MANUAL
AOS WPC - Tech Training 6 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
UIM - USER INTERFACE MODULE - STATUS LIGHTS
LCD display
4 line x 20 character
System Status
Firing Rate
LEDs
5 Touch Sensitive
User Input Buttons
System Status LED Lights
Firing Rate Status
The three “System Status” LED lights on the upper
right portion of the UIM convey current operational
and diagnostic information.
The red Service LED will be continuously illuminated
for soft lock-outs and flashing on and off for hard lock-
outs.
Soft lock-outs will automatically reset after the condition that caused the error has been
corrected or a factory programmed time period of one hour. Soft lock-outs can also be reset
by touching the Select button while the error screen is displayed.
Hard lock-outs can only be reset by touching the Select button while the error screen is
displayed. Power interruptions or cycling the power on and off will not reset hard or
soft lock-outs.
The yellow Standby LED is illuminated whenever the system set point has been satisfied.
The green Running LED is illuminated continuously whenever a call for heat is active.
The Firing Rate Status indicator shows the current
firing rate of the boiler between; 25 and 100%.
The Firing Rate Status indicator will not illuminate
unless flame is proven by one of the two flame
sensors; high fire sensor/low fire sensor.
Status

AOS WPC - Tech Training 7 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
VF BOILER SERVICE MANUAL
UIM - USER INTERFACE MODULE - USER INPUT BUTTONS
Select Button is used to:
• Enter menu screens.
• Activate adjustment mode for various settings. The [ >] will be flashing
slowly to the left of the menu item when the adjustment mode is active.
• Confirm and store new values and settings in memory.
• Reset the control when in a lock-out condition.
Menu Button is used to:
• Display a list of available menu screens.
• Abort or cancel new values and settings, returning to last saved value.
Help Button is used to:
• Touch once to display helpful information about the current menu screen.
Touch a second time to return to previous screen.
• Touched from the main menu screen and the UIM displays general
information on how to use the EMC 5000 user interface.
Up and Down Buttons are used to:
• Scroll or navigate up and down lists of menu screens and menu items.
When the current menu contains more than four lines of text, Up and
Down arrows will appear on the right side of the LCD screen indicating
more information is available off screen.
• Change values for user settings when adjustment mode has been
activated by pressing the Select button. (Select button must be touched
once more to confirm and store the new value in memory)
LCD display
4 line x 20 character
System Status
Firing Rate
LEDs
5 Touch Sensitive
User Input Buttons
Status

VF BOILER SERVICE MANUAL
AOS WPC - Tech Training 8 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
UIM - USER INTERFACE MODULE - CHANGING SETTINGS
1
2
3
4
5
6
The sequence of UIM screen displays below is an example of how to navigate the menus to change
the Operating Set Point.
Screen Display 1: shows the temperatures screen. This is the default display screen the UIM comes
to rest at after approximately 60 seconds without any user input. The Menu button is touched once
to enter the Menus screen containing 9 different sub menus.
Screen Displays 2 - 4: show the first four lines of the Menus screen. The Down button is touched
several times to navigate to the User Settings menu on line four. The [ >] sign on the left moves
down one line each time the down button is touched. Also notice the down arrow that appears on
the lower right corner, this indicates there are more menu items below the four lines currently being
displayed. Up arrows appear on the top right corner when there are more menu items above.
Screen Display 5: the Select button is touched once to enter the User Settings menu.
Screen Display 6: shows the first four lines of the User Settings menu. Touching the Select button
while the [ > ] sign is lined up with the “Oper Setpnt” menu item activates the adjustment mode for
this menu item. (Oper Setpnt = Operating Set Point)
The Operating Set Point can now be changed. The [ >] sign begins to flash on and off slowly
indicating the adjustment mode is active for this setting. Touching the Up button once at this point
would change the Operating Set Point 1 degree higher. Touching the Down
button once would lower the setting by 1 degree. Touch the Up or Down
button continuously and the setting will start to ramp up or down rapidly.
Release the Up or Down button when the desired setting is reached.
Touch the Select button once to confirm and store the new value in memory.

AOS WPC - Tech Training 9 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
VF BOILER SERVICE MANUAL
UIM - USER INTERFACE MODULE - MENU SCREENS
At the top center of the UIM panel is the display LCD. This LCD is used to provide
information to the user through menu activated screens. Within each of the screens, helpful
context sensitive information can be displayed at any time by touching the “Help” button.
Touching the help button once more returns the user to the previous screen.
The 10 available screens are:
Menu Screen:
Displayed when the “Menu” button is touched. This screen is the selection point for the other
menu screens.
Temperatures Screen (Default Screen):
Displays the temperatures sensed from the Outlet, Inlet, and optional remote Tank/Loop
temperature probes. This screen also displays the calculated temperature rise (Outlet minus
Inlet) through the boiler, sometimes referred to as the Delta T (ΔT). Shorted and
disconnected probes will have “Short” and “----” displayed to the right. The Temperatures
Screen is the default screen the boiler will come to rest at without any user input for
approximately 60 seconds.
There are no adjustable user inputs available from this screen.
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 fulfilled). For
example; if water is flowing, as detected by the flow switch, an asterisk (*) will appear in front
of the Flow label (IE: *Flow).
There are no adjustable user inputs available from this screen.
Control States Screen:
The CCB/FCB operating states of the boiler are displayed in this menu screen along with the
actual blower motor rpm as relayed from a Hall Effect sensor (page 13) located inside the
end cap of the blower motor. Blower rpm are displayed in real time. CCB and MCB are the
same component on VF Boilers. See explanation for this and the FCB term on page 25.
There are no adjustable user inputs available from this screen.
User Settings Screen:
This screen is used to enter values for various user settings such as; the operating set point
abbreviated Oper Setpnt, the Hi Limit (automatic high limit), pump post circulate time etc.
The Select button must be touched once to activate the adjustment mode for a user setting
and again to confirm and store the new setting into memory.
Configuration Settings Screen
Displays the status of the SW1 and SW2 dip switches (pages 30 and 33) on the MCB.
There are no adjustable user inputs available from this screen.