A.O. Smith XWH 150 How to use

COMMERCIAL GAS WATER HEATERS
Service Handbook
PRINTED IN THE U.S.A. 1119 100274940_2000534998_Rev B
500 Tennessee Waltz Parkway
Ashland City, TN 37015
FOR MODELS:
XWH 150 THRU 800
INSTALLATION CONSIDERATIONS - PRE SERVICE CHECKS -
CONSTRUCTION - OPERATION & SERVICE - TROUBLESHOOTING
SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE TECHNICIAN

1
TABLE OF CONTENTS
INTRODUCTION.......................................................................................2
Qualifications ........................................................................................2
Service Warning ...................................................................................2
Service Reminder .................................................................................2
Tools Recommended............................................................................2
INSTALLATION CONSIDERATIONS ........................................................3
Instruction Manual ................................................................................3
Closed Water Systems .........................................................................3
Thermal Expansion...............................................................................3
Air Requirements..................................................................................3
Contaminated Air ..................................................................................3
PLEASE READ BEFORE PROCEEDING.................................................4
Handling Ceramic Fiber Materials ........................................................4
USER INTERFACE MODULE (UIM)/ TOUCH SCREEN DISPLAY ..........5
CONTROL INPUTS...................................................................................6
CONTROL OUTPUTS...............................................................................7
GENERAL OPERATION............................................................................8
How The Water Heater Operates .........................................................8
Sequence Of Operation........................................................................8
Access Modes ......................................................................................8
Saving Parameters ...............................................................................8
SEQUENCE OF OPERATION ..................................................................9
TOUCH SCREEN DISPLAY MENU ACCESS.........................................11
TOUCH SCREEN DISPLAY PARAMETER ACCESS .............................13
PARAMETER TABLE ..............................................................................14
VIEWABALE AND CHANGEABLE CONTROL PARAMETERS..............16
Temperature .......................................................................................16
Service................................................................................................16
Circulation Pumps ..............................................................................17
Building Management System (BMS).................................................17
Lead/Lag ............................................................................................18
Economy Mode/Clock.........................................................................19
Short Cycling ......................................................................................20
MAINTENANCE ......................................................................................21
Maintenance Schedules .....................................................................21
Maintenance .......................................................................................22
TROUBLESHOOTING ............................................................................27
Troubleshooting Chart - Not Visible On Display .................................28
Troubleshooting Chart - Noisy System ...............................................29
Troubleshooting Chart - Fault Messages Displayed...........................30
Checking Temperature Sensors .........................................................38
Combustion Analysis Procedure.........................................................39
Gas Valve Adjustment Procedure .......................................................40

2Servicing should only be performed by a Qualified Service Technician
INTRODUCTION
This Service Handbook covers the water heater Model and Series numbers listed on the front cover only.
The instructions and illustrations contained in this service handbook will provide you with troubleshooting
procedures to verify proper operation and diagnose and repair common service problems.
QUALIFICATIONS
QUALIFIED INSTALLER OR SERVICE AGENCY
Installation and service of this water heater requires ability equivalent to that of a Qualified Agency (as defined
by ANSI below) in the field involved. Installation skills such as plumbing, air supply, venting, gas supply and
electrical supply are required in addition to electrical testing skills when performing service.
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 qualified (as defined by ANSI above) and licensed or certified as required by the authority
having jurisdiction to perform a given task do not attempt to perform any of the procedures described in this
service handbook. If you do not understand the instructions given in this service handbook do not attempt to
perform any procedures outlined in this service handbook.
SERVICE REMINDER
When performing any troubleshooting step outlined in this service handbook 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.
TOOLS RECOMMENDED
• Instruction Manual that came with the water heater.
• All tools common to installation and service of commercial water heaters such as hand tools, screwdrivers,
pipe wrenches etc.
• Long (8-10”) T handle 1/8 inch hex (allen key) wrench for Combustion Blower removal and installation.
• Hex (Allen) wrench sizes: 5/32”, 1/8”, 1/4” and 5/16" - for Burner, and 24 Volt Gas Control Valve removal
and installation.
• Digital manometer: Range -20.00 to +20.00" W.C. Resolution - 0.01" W.C. Required to test pressure
switch performance and supply gas pressure.
• Digital Multi Meter; capable of measuring:
• AC/DC Voltage.
• Ohms.
• DC micro amps (μA).

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Servicing should only be performed by a Qualified Service Technician
INSTALLATION CONSIDERATIONS
This section of the Service Handbook covers some of the critical installation requirements that, when
overlooked, often result in operational problems, down time and needless parts replacement. Costs to
correct installation errors are not covered under the limited warranty. Ensure all installation requirements and
instructions contained in the Instruction Manual that came with the water heater have been followed prior to
performing any service procedures.
INSTRUCTION MANUAL
Have a copy of the Instruction Manual that came with the water heater on hand for the model and series
number being serviced. Installation information given in this Service Handbook is not a complete installation
instruction. Installation information given in this Service Handbook has a limited focus as it applies to servicing
the water heater. This Service Handbook does not replace or supersede the Instruction Manual that came
with the water heater. Always refer to the Instruction Manual for complete installation instructions. If the
Instruction Manual is not on hand, copies can be obtained from the manufacturers web site or by calling the
technical support phone number shown on the back cover of this Service Handbook.
CLOSED WATER SYSTEMS
Water supply systems may, because of code requirements or such conditions as high line pressure, among
others, have installed devices such as pressure reducing valves, check valves, and back flow preventers.
Devices such as these cause the water system to be a closed system.
THERMAL EXPANSION
As water is heated, it expands (thermal expansion). In a closed system the volume of water will grow when
it is heated. As the volume of water grows there will be a corresponding increase in water pressure due to
thermal expansion. Thermal expansion can cause premature tank failure (leakage). This type of failure is not
covered under the limited warranty. Thermal expansion can also cause intermittent Temperature-Pressure
Relief Valve operation: water discharged from the valve due to excessive pressure build up. This condition
is not covered under the limited warranty. The Temperature-Pressure Relief Valve is not intended for the
constant relief of thermal expansion.
A properly sized thermal expansion tank must be installed on all closed systems to control the harmful effects
of thermal expansion. Contact a local plumbing service agency to have a thermal expansion tank installed.
AIR REQUIREMENTS
Carefully review the requirements for combustion and ventilation air in the Instruction Manual that came
with the water heater. Failure to meet these requirements when the water heater is installed or overlooking
their importance when servicing the water heater often results in needless down time, unnecessary parts
replacement, and customer dissatisfaction.
An inadequate supply of air for combustion and ventilation often causes operational problems. A lack of
combustion and ventilation air can create a negative ambient air pressure in the installed space which can
lead to improper combustion and operational problems with pressure switches.
CONTAMINATED AIR
Combustion air that is contaminated can greatly diminish the life span of the water heater and water heater
components such as Igniters and Burners. Propellants of aerosol sprays, beauty shop supplies, water softener
chemicals and chemicals used in dry cleaning processes that are present in the combustion, ventilation or
ambient air can cause such damage.
Vapors from volatile compounds such as solvents, cleaners, chlorine based chemicals and refrigerants in
addition to being highly flammable in many cases, can also react to form highly corrosive substances such
as acids inside the combustion chamber. The results can be hazardous and cause product failure.
If the water heater is installed in beauty shops, barber shops or laundries with dry cleaning equipment, it is
imperative the water heater be installed in a Direct Vent configuration so that air for combustion is derived
directly from the outdoor atmosphere through a sealed intake air pipe. See the venting installation section
in the Instruction Manual that came with the water heater for more information on Direct Vent installations.

4Servicing should only be performed by a Qualified Service Technician
PLEASE READ BEFORE PROCEEDING
Installer – Read all instructions, including this Service Handbook and the XP Water Heater Instruction Manual,
before installing. Perform steps in the order given. Have this water heater serviced/inspected by a qualified
service technician at least annually. Failure to comply with the above could result in severe personal injury,
death or substantial property damage.
HANDLING CERAMIC FIBER MATERIALS
REMOVAL OF COMBUSTION CHAMBER LINING
The combustion chamber insulation in this appliance contains ceramic fiber material. Ceramic fibers can
be converted to cristobalite in very high temperature applications. The International Agency for Research
on Cancer (IARC) has concluded, “Crystalline silica in the form of quartz or cristobalite from occupational
sources is carcinogenic to humans (Group 1)”. Normal operating temperatures in this appliance are below
the level to convert ceramic fibers to cristobalite. Abnormal operating conditions would have to be created to
convert the ceramic fibers in this appliance to cristobalite. The ceramic fiber material used in this appliance
is an irritant; when handling or replacing the ceramic materials it is advisable that the installer follow these
safety guidelines.
• Avoid breathing dust and contact with skin and eyes.
• Use NIOSH certified dust respirator (N95). This type of respirator is based on the OSHA
requirements for cristobalite at the time this document was written. Other types of respirators may
be needed depending on the job site conditions. Current NIOSH recommendations can be found
on the NIOSH website at http://www.cdc.gov/niosh/homepage.html. NIOSH approved respirators,
manufacturers, and phone numbers are also listed on this website.
• Wear long-sleeved, loose fitting clothing, gloves, and eye protection.
• Apply enough water to the combustion chamber lining to prevent airborne dust.
• Remove the combustion chamber lining from the water heater and place it in a plastic bag for
disposal.
• Wash potentially contaminated clothes separately from other clothing. Rinse clothes washer
thoroughly.
NIOSH stated First Aid.
• Eye: Irrigate immediately.
• Breathing: Fresh air.
Note: When calling or writing about the water heater – Please have the water heater model and serial
number from the water heater rating plate. Consider piping and installation when determining water
heater location (see the XP Water Heater Instruction Manual). Any claims for damage or shortage in
shipment must be filed immediately against the transportation company by the consignee.
When servicing water heater –
• To avoid electric shock, disconnect electrical supply before performing maintenance.
• To avoid severe burns, allow the water heater to cool before performing maintenance.
Water heater operation –
• Do not block flow of combustion or ventilation air to the water heater.
• Should overheating occur or gas supply fail to shut off, do not turn off or disconnect electrical supply
to circulator. Instead, shut off the gas supply at a location external to the appliance.
• Do not use this water heater if any part has been under water. The possible damage to a flooded
appliance can be extensive and present numerous safety hazards. Any appliance that has been
under water must be replaced.

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Servicing should only be performed by a Qualified Service Technician
USER INTERFACE MODULE (UIM)/ TOUCH SCREEN DISPLAY
Tank Temperature 71°F
Operating Setpoint 184°F
Status: Ignition
HELPDISABLE
A. O. Smith XP
MENU
OFF
GAS
O
N
LCD Touch
Screen Display
Status Icons
Main Menu Help MenuEnable / Disable / Reset
Button
Figure 1. User Interface Module (UIM)/ Touch Screen Display

6Servicing should only be performed by a Qualified Service Technician
CONTROL INPUTS
GAS PRESSURE SWITCH
DHW THERMOSTAT
FLOW SWITCH
TANK SENSOR
SEQUENCER / BUILDING
MANAGEMENT SYSTEM
LOW VOLTAGE
CONNECTION
BOARD
INLET TEMPERATURE
SENSOR
OUTLET TEMPERATURE
SENSOR
FLUE GAS SENSOR
DAMPER PROVING SWITCH
FLAME SENSOR
LOW WATER CUTOFF
BLOCKED CONDENSATE
SWITCH
TOUCH SCREEN
DISPLAY
CONTROL BOAR
D
AIR PRESSURE SWITCH
O-TEMP
HEAT EXCHANGER SWITCH
DOOR TEMPERATURE SWITCH
AIN ADAPTER
CABLE
Figure 2. UIM Control Inputs

7
Servicing should only be performed by a Qualified Service Technician
CONTROL OUTPUTS
LOW VOLTAGE
CONNECTION
BOARD
CONTROL BOARD
ALARM BELL
DAMPER RELAY
RUN TIME CONTACTS
SEQUENCER / BUILDING
MANAGEMENT SYSTEM
WATER HEATER PUMP
IGNITER
BLOWER
GAS VALVE
TOUCH SCREEN
DISPLAY
BUILDING RECIRCULATION
PUMP
AIN ADAPTER
CABLE
Figure 3. UIM Control Outputs

8Servicing should only be performed by a Qualified Service Technician
GENERAL OPERATION
HOW THE WATER HEATER OPERATES
The XP water heater uses an advanced stainless steel heat exchanger and an electronic control module that
allows fully condensing operation. The blower pulls in gas and air and pushes flue products out of the water
heater through the heat exchanger and flue piping. The control module regulates blower speed to control
water heater firing rate. The gas valve senses the amount of air flowing into the water heater and allows only
the right amount of gas to flow.
SEQUENCE OF OPERATION
Table 1 shows control module normal sequences of operation for water heating operation.
ACCESS MODES
User
The user can adjust tank target temperatures by accessing the Tank Temperature using the MENU option on
the Touch Screen Display. The date and time can also be changed.
Installer
Most parameters are available only to the installer, accessible by entering the installer password (5309).
SAVING PARAMETERS
Refer to the Parameter Table - Table 4 on Pages 14 and 15 of this Service Handbook.
To save parameters and exit programming:
After setting or changing the parameters touch the ACCEPT option on the Touch Screen Display.
To enter a parameter and continue programming:
Use the +/ - options for setting the required parameters or the Up/ Down arrows on the Touch Screen Display
to access and make appropriate changes. Remember to ACCEPT the changes when finished programming
in order to save the changes made.

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Servicing should only be performed by a Qualified Service Technician
SEQUENCE OF OPERATION
Table 1. Sequence Of Operation
OPERATION TOUCH SCREEN DISPLAY
The control will turn on the water heater pump
(always ON except in Setpoint Adjustment). The
flow switch and/or LWCO must close.
The control turns on power to the damper relay.
The damper proving switch, air pressure switch,
and blocked drain switch must close.
The control starts the prepurge cycle.
The control starts the trial for ignition by energizing
the spark electrode and opening the gas valve.
Tank Temperature 90°F
Operating Setpoint 93°F
Status: Pre-Purge
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 92°F
Operating Setpoint 93°F
Status: Standby
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 92°F
Operating Setpoint 93°F
Status: Standby
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 90°F
Operating Setpoint 93°F
Status: Ignition
HELPDISABLE
A. O. Smith XP
MENU
OFF
GAS
O
N

10 Servicing should only be performed by a Qualified Service Technician
OPERATION TOUCH SCREEN DISPLAY
If flame is not detected after the sparking ends
(approximately 5 seconds), the control will perform
a postpurge, then start another prepurge cycle
and try to light the burner again. On the 500 and
larger models, the control will lock out if this second
attempt fails. On the 400 and smaller models, the
control will perform a total of 4 attempts before
locking out.
If flame is detected, it holds the firing rate steady
for a few seconds to let the flame stabilize, then it
begins to modulate the firing rate based on a set
point or some other command (such as a 0-10V
BMS signal).
Once the call for heat is satisfied, the control will
de-energize the gas valve. The blower will continue
to run for approximately 12 seconds during the
postpurge.
The water heater pump will continue to run for its
respective pump delay time before turning off. A 60
second short cycle period will start, which will delay
any new call for heat until it times out.
In Standby, ready to start a new cycle.
Table 1. Sequence Of Operation (Continued.)
Tank Temperature 90°F
Operating Setpoint 93°F
Status: Post-Purge
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 92°F
Operating Setpoint 93°F
Status: Short Cycling
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 92°F
Operating Setpoint 93°F
Status: Standby
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 90°F
Operating Setpoint 93°F
Status: Post-Purge
HELPDISABLE
A. O. Smith XP
MENU
Tank Temperature 90°F
Operating Setpoint 93°F
Status: Heating
HELPDISABLE
A. O. Smith XP
MENU
OFF
GAS
O
N

11
Servicing should only be performed by a Qualified Service Technician
TOUCH SCREEN DISPLAY MENU ACCESS
Table 2. Menus From The Touch Screen Display
OPERATION TOUCH SCREEN DISPLAY
The home screen of the User Interface Module Touch
Screen Display shows Tank Temperature, Operating
Setpoint, Unit Status, MENU option, ENABLE/
DISABLE option and HELP option.
The ENABLE/ DISABLE button shows whether the
unit is in On/ Off position.
Press the MENU options to get access to Main Menu
which includes Temperatures, Heater Status, Display
Settings, Heater Information etc.
Use the appropriate Menu option to change unit
settings or for any other unit information.
Tank Temperature 92°F
Operating Setpoint 93°F
Status: Standby
HELPDISABLE
A. O. Smith XP
MENU
Temperatures >
Heater Status >
Display Settings >
Heater Information >
Current Fault (VIEW) >
HELPBACK
Main Menu
Fault History >
Fault Occurrence >
Service >
Circulation Pumps >
Building Management >
HELPBACK
Main Menu
Building Management >
Lead/Lag >
Economy Mode/Clock >
Short Cycling >
Restore Defaults >
HELPBACK
Main Menu

12 Servicing should only be performed by a Qualified Service Technician
OPERATION TOUCH SCREEN DISPLAY
Press the HELP options to get additional information
related to Operating Instructions, Status Icon Legend,
Operating States etc.
Table 2. Menus From The Display Panel (Continued.)
Operating Instructions >
Status Icon Legend >
Operating States >
Adjusting Operating Setpoint >
Change the Display Units >
Restore Defaults >
BACK
Help Menu
Status Icon Legend >
Operating States >
Adjusting Operating Setpoint >
Change the Display Units >
Restore Defaults >
Contact Information >
BACK
Help Menu

13
Servicing should only be performed by a Qualified Service Technician
TOUCH SCREEN DISPLAY PARAMETER ACCESS
The Home Screen for the Touch Screen Display shows the MENU button to access additional user and
installer screens. Parameters that can be accessed are indicated by a ' > ' to the right of the screen.
Table 3. Access Parameters From The Display Panel
OPERATION UIM DISPLAY
From the home screen of the User Interface Module
touch the MENU option.
Under the MENU select Temperatures.
Select the Tank Setpoint under the Temperatures
parameters screen.
Adjust the Tank Setpoint using the +/ - buttons on the
Touch Screen Display to the desired temperature.
Select Accept button to save the desired temperature
settings.
The UIM will save the desired temperature settings
and shows Complete on the screen before displaying
back the Temperatures parameters screen.
Tank Temperature 92°F
Operating Setpoint 93°F
Status: Standby
HELPDISABLE
A. O. Smith XP
MENU
Temperatures >
Heater Status >
Display Settings >
Heater Information >
Current Fault (VIEW) >
HELPBACK
Main Menu
Tank Setpoint 141°F >
Differential 6°F >
Tank Temperature Open
Probe Offset 4°F >
Outlet Temperature 70°F
Inlet Temperature 70°F
BACK
Temperatures
HELP
141°F
MIN MAX
60°F 185°F
BACK
Tank Setpoint
ACCEPT
+
–
141°F
MIN MAX
60°F 185°F
Tank Setpoint
Complete

14 Servicing should only be performed by a Qualified Service Technician
PARAMETER TABLE
This table lists User Interface Module control parameters and where to access them.
Table 4. UIM Parameters
MENU ACCESS LOCATION/
PARAMETER NAME
USER ACCESS INSTALLER ACCESS
DISPLAY MODIFY DISPLAY MODIFY
Temperatures Temperatures> Tank Setpoint YES YES YES YES
Temperatures> Differential YES NO YES YES
Temperatures> Setpoint Offset YES NO YES YES
Display
Settings
Display Settings> Backlight Delay YES NO YES YES
Display Settings> Temperature Units YES YES YES YES
Display Settings> Backlight Delay YES NO YES YES
Service Service>Service Log> CLEAR button YES NO YES YES
Service> Service Contact Info> Contact
Name YES NO YES YES
Service> Service Contact Info> Contact
Phone YES NO YES YES
Circulation
Pumps
Circulation Pumps> DHW Pump Delay YES NO YES YES
Circulation Pumps> DHW Anti-Seize YES NO YES YES
Building
Management
Building Management> BMS Tstat Input YES NO YES YES
Building Management> BMS YES NO YES YES
Building Management> BMS Type YES NO YES YES
Building Management> Volts at Min YES NO YES YES
Building Management> Volts at Max YES NO YES YES
Building Management> Rate at Min Volts YES NO YES YES
Building Management> Rate at Max Volts YES NO YES YES
Building Management> Setpoint at Min
Volts YES NO YES YES
Building Management> Setpoint at Max
Volts YES NO YES YES
Building Management> On Volts YES NO YES YES
Building Management> Off Differential
Volts YES NO YES YES

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Servicing should only be performed by a Qualified Service Technician
MENU ACCESS LOCATION/
PARAMETER NAME
USER ACCESS INSTALLER ACCESS
DISPLAY MODIFY DISPLAY MODIFY
Lead/Lag Lead/Lag> Address YES NO YES YES
Lead/Lag> Type YES NO YES YES
Lead/Lag> Max Setpoint YES NO YES YES
Lead/Lag> Min On/Off Time YES NO YES YES
Lead/Lag> Min Next On Time YES NO YES YES
Lead/Lag> DHW Size (Slave X) YES NO YES YES
Economy
Mode/ Clock
Economy Mode/Clock > Current Time YES YES YES YES
Economy Mode/Clock > Current Date YES YES YES YES
Economy Mode/Clock> Setpoint
Adjustment YES NO YES YES
Economy Mode/Clock> Start Time X YES NO YES YES
Economy Mode/Clock> Stop Time X YES NO YES YES
Short Cycling Short Cycling> Short Cycling Time YES NO YES YES
Short Cycling> Short Cycling Differential YES NO YES YES
Short Cycling> Ramp Delay Step X Time YES NO YES YES
Short Cycling> Ramp Delay Step X %
Rate YES NO YES YES
Table 4. UIM Parameters (Continued.)

16 Servicing should only be performed by a Qualified Service Technician
VIEWABALE AND CHANGEABLE CONTROL PARAMETERS
Before changing parameters, note the settings so that the unit can be returned to its original operating
parameters.
TEMPERATURE
Tank Setpoint
By installing a tank sensor, the UIM control can perform the tank thermostat function. The UIM control
automatically detects the presence of this sensor, and generates a DHW call for heat when the tank
temperature drops below the tank setpoint differential (Tank Setpoint Differential parameter), and finishes the
call for heat when the tank temperature reaches tank set point + offset. This parameter can be changed by
the installer by accessing the Tank Setpoint parameter. The default value is 125°F (52°C).
Differential
When a tank sensor is installed, the tank temperature must drop this amount below the tank setpoint before
the water heater turns back on. The installer can adjust this setting by accessing the Differential parameter.
The minimum setting is 0° (0°C), and the maximum is 40°F (22°C). The default setting is 6°F (3°C). This
parameter can only be changed by the installer by accessing the Differential parameter.
Setpoint Offset
The tank setpoint offset measures how far the actual temperature must go above the setpoint before the call
for heat ends (the water heater will turn off). This parameter can be changed by the installer by accessing the
Setpoint Offset parameter. The temperature range of this parameter is 0°F (0°C) to 10°F (30°C). The default
value is 4°F (6°C).
DISPLAY SETTINGS
Backlight Delay
This is the time in which the display remains illuminated. The range is 30 seconds to 5 minutes. The default
is 3 minutes.
Temperature Units (°C / °F)
The control can be configured to display temperature in either °C or °F. This parameter can be changed by
the user or the installer by accessing the Temperature Units parameter. The default is °F.
HEATER INFORMATION
UIM Version
The software version allows the user to view the software version in use by the control. This software controls
the operation of the water heater. When a new software version becomes available, the existing control can
be replaced with a new control to update the software. Software version is read only.
FAULT HISTORY
CLEAR Button
The CLEAR function clears the last 10 errors log.
SERVICE
Service Mode Delay
While in Service Mode, the unit will override all other heat demands. The Service Mode allows the installer
to set the unit to any firing rate for the purpose of combustion analysis. The delay sets the length of time the
water heater will stay in the Service Mode if no keys have been pressed before going back to its original
state. This parameter can only be changed by the installer by accessing the Service Mode Delay parameter.
The time range of this parameter is 1 to 10 minutes. The default value is 10 minutes.
Service Contact Info - Contact Name & Contact Phone
This can be programmed to access the Contact Name and Contact Phone parameter.

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Servicing should only be performed by a Qualified Service Technician
CIRCULATION PUMPS
DHW Pump Delay
The DHW pump delay parameter sets the length of time the DHW pump (if connected) will run after a DHW
demand has been satisfied. This parameter is adjustable by the installer by accessing the DHW Pump Delay
parameter. The time range for this parameter is 10 seconds to 40 minutes. The default time is 1 minute.
DHW Anti-Seize
If the water heater pump does not run for 24 hours, it will be turned on briefly to prevent it from seizing. The
length of time it runs is determined by the DHW Pump Anti-Seize Delay parameter. The range of this setting
is 0 seconds to 50 minutes. The default setting is 20 seconds.
BUILDING MANAGEMENT SYSTEM (BMS)
BMS Tstat Input
When controlling the water heater through the 0 - 10V BMS input or through ModBus, the water heater can
be enabled one of two ways. With the BMS Thermostat Input parameter set to ACTIVE, the water heater will
be enabled by closing the tank thermostat input. When set to INACTIVE, the water heater will be enabled by
the voltage level on the 0 - 10V input (in the case of 0 - 10V BMS control), or the 0 - 10V input value received
through ModBus. The default value is INACTIVE.
BMS
The set point or modulation of the water heater may be controlled through the 0 - 10V BMS input or through
ModBus. When the BMS parameter is set to INACTIVE, the 0 - 10V input will be ignored. When set to
ACTIVE, the set point or modulation will be controlled by the voltage on the 0 - 10V input (in the case of
0 - 10V BMS control), or the 0 - 10V input value received through ModBus. The default value is INACTIVE.
BMS Type
When programmed for BMS control through the 0 - 10V BMS input or through ModBus, the 0 - 10V signal
can be interpreted as either a modulation command or a set point. When the BMS Type parameter is set to
POWER, the 0 - 10V signal will control the modulation. When set to SETPOINT, the 0 - 10V signal will control
the tank set point. The default setting is SETPOINT.
Volts at Min
When programmed for BMS control through the 0 - 10V BMS input or through ModBus, the Volts at Minimum
parameter should be set to the minimum voltage signal sent to the SMART SYSTEM control. The range of
this parameter is 0.0V to 10.0V Volts. The default setting is 2.0V.
Volts at Max
When programmed for BMS control through the 0 - 10V BMS input or through ModBus, the Volts at Maximum
parameter should be set to the maximum voltage signal sent to the SMART SYSTEM control. The range of
this parameter is the Volts at Minimum value to 10.0V. The default value is 10.0V.
Rate at Min Volts
When programmed for BMS control through the 0 - 10V BMS input or through ModBus and the BMS Type
is programmed as POWER, the modulation percentage represented by the Volts at Minimum parameter is
set by the Rate at Minimum Volts parameter. The minimum value is 0% and the maximum is the Rate at
Maximum Volts setting. The default value is 20%.
Rate at Max Volts
When programmed for BMS control through the 0 - 10V BMS input or through ModBus and the BMS Type is
programmed as POWER, the modulation percentage represented by the Volts at Maximum parameter is set
by the Rate at Maximum Volts parameter. The minimum value is the Rate at Minimum Volts setting and the
maximum is 100%. The default value is 100%.

18 Servicing should only be performed by a Qualified Service Technician
Setpoint at Min Volts
When programmed for BMS control through the 0 - 10V BMS input or through ModBus and the BMS Type is
programmed as SETPOINT, the set point represented by the Volts at Minimum parameter is set by the Set
Point at Maximum Volts parameter. The minimum value is 32°F (0°C) and the maximum is the Set Point at
Maximum Volts setting. The default value is 70°F (21°C).
Setpoint at Max Volts
When programmed for BMS control through the 0 - 10V BMS input or through ModBus and the BMS Type is
programmed as SETPOINT, the set point represented by the Volts at Maximum parameter is set by the Set
Point at Maximum Volts parameter. The minimum value is the Set Point at Minimum Volts setting and the
maximum is 190°F (88°C). The default value is 180°F (82°C).
On Volts
When programmed for BMS control through the 0 - 10V BMS input or through ModBus and the BMS
Thermostat Input is set to INACTIVE, the On Volts parameter determines the 0 - 10V BMS input voltage at
which the water heater is enabled. The minimum value is 0.5V and the maximum is 10.0V. The default value
is 2.0V.
Off Differential Volts
When programmed for BMS control through the 0 - 10V BMS input or through ModBus and the BMS
Thermostat Input is set to INACTIVE, the Off Differential Volts parameter determines how far below the On
Volts setting the 0 - 10V BMS input voltage must be in order to disable the water heater. The minimum value
is 0.2V and the maximum is the On Volts setting. The default value is 1.0V.
LEAD/LAG
Address
The water heater designated as the Leader needs to be programmed with address 0. All the Member water
heaters require addresses from 1 to 7, and the addresses must be different for each Member. The addresses
can be in any order, regardless of the order in which the units are wired together. This parameter is adjustable
by the installer by accessing the Lead/Lag Address parameter. The tank sensor must be connected to the
Leader water heater. The default address is 1.
Lead/Lag/ Efficiency Enhancement Types
There are two (2) options for the way a Lead/Lag divides the load between its heaters. The first is Lead/Lag,
designated as L/L in the menu. This method is used when it is desired to have the least amount of total flow
through the water heaters. This method will modulate the last two (2) water heaters. This provides for smooth
transitions when a water heater turns on or off. When the last water heater reaches 100% and the calculated
load is still increasing, it will start the next water heater at 20% and reduce the previous water heater to 80%,
thus eliminating the sudden jump in total output of the Lead/Lag. When the calculated load is decreasing
and the last water heater gets down to 20% fire, it will hold it there and start lowering the firing rate on the
next-to-last water heater. When the next-to-last water heater reaches 20%, it will turn the last water heater
off and raise the rate of the next-to-last water heater to 40%, thus eliminating the sudden drop in total output
of the Lead/Lag.
The other Lead/Lag divider method is Efficiency Enhancement, designated as Efficiency in the menu. This
method is used, as the name implies, when it is desired to have the most efficient system. When the first
water heater reaches a certain rate (default = 90%), it lowers its rate to 45% and turns on the next water
heater at 45%. The two (2) water heaters then modulate at the same rate.
As the calculated load increases further and both water heaters ramp up to 90%, it lowers the rate of the first
two (2) water heaters to 60% and brings the next water heater on at 60%. The three (3) water heaters then
modulate together. As the calculated load decreases, the water heaters will reach a lower threshold (default =
30%), at which time the last water heater (the third in our example) will turn off and the Lead/Lag will increase
the rates of the remaining water heaters to provide the equivalent total output as before ((3 x 30%) / 2 = 45%
in our example).
Efficiency Enhancement is automatically selected when heaters of different sizes are programmed into the
Leader water heater (see DHW Size on Page 19).

19
Servicing should only be performed by a Qualified Service Technician
Max Setpoint
This parameter determines the set point used by the individual water heaters in a Lead/Lag. When a water
heater is commanded to fire by the Leader water heater, it will attempt to achieve this temperature at its outlet.
The Leader water heater will limit the modulation of the water heaters in order to hold the temperature at the
tank sensor to the user set point. If any of the water heater outlet temperatures reach the maximum Lead/Lag
setpoint, the water heater will then modulate down on its own in order to keep its outlet temperature within
the maximum Lead/Lag setpoint. Therefore, this parameter can be used to limit the outlet temperatures of all
the water heaters in a Lead/Lag. This parameter is adjustable by the installer by accessing the Max Setpoint
parameter under the Control Modes and then Lead/Lag. The temperature range of this parameter is 32°F
(0°C) to 190°F (88°C). The default maximum setpoint is 185°F (85°C).
Min On/Off Time
In order to prevent units in a Lead/Lag from short cycling, this parameter defines the minimum ON and OFF
time for each unit. The installer can adjust this time by accessing the Minimum On/Off Time parameter. The
minimum setting is 0 seconds and the maximum setting is 10 minutes. The default is 30 seconds.
Min Next On Time
In order to reduce the risk of temperature overshoot with a Lead/Lag, this parameter defines the minimum
time delay from starting one unit until the next unit may be started. The installer can adjust this time delay
by accessing the Minimum Next On Time parameter. The minimum setting is 0 minutes and the maximum
setting is 10 minutes. The default is 60 seconds.
DHW Size (Slave X)
When water heaters of different sizes are connected together in a Lead/Lag, the Leader water heater has
to know the size of each heater in that Lead/Lag. The water heater size parameters allow the installer to
program the sizes based on the Lead/Lag address. This screen shows the Lead/Lag address and the size of
the water heater with that address (in BTU/hr):
The UIM control automatically uses the Efficiency Enhancement Lead/Lag type when controlling water
heaters of different sizes.
ECONOMY MODE/CLOCK
Time and Date
The control uses an internal clock for the night setback feature and for logging of events. For these features
to work correctly, the clock must be set when the water heater is first installed or anytime the water heater has
been powered off for more than four (4) hours. This parameter must be accessed to set the clock.
Note: The internal clock does not adjust for Daylight Savings Time and therefore, will require a manual
adjustment.
Setpoint Adjustment
Once the unit’s internal clock has been set correctly, the Setpoint Adjustment feature can be used to program
a lower setpoint during unoccupied times. The DHW can be programmed for night setback. When in night
setback, the control reduces the set point by a fixed amount. For DHW, it subtracts the DHW Setpoint
Adjustment offset from the tank set point (Tank Set point parameter).
Note: The DHW Setpoint Adjustment will not work without a tank sensor installed.
The installer may adjust the Setpoint Adjustment by accessing the Economy Mode parameter. The minimum
setting is 0°F (0°C) and the maximum setting is 90°F (50°C).
Start Time X/ Stop Time X
This is the time in which the Setpoint Adjustment becomes active. There are 7 start times and 7 stop times
each for the DHW night setback feature. The DHW Night Setback On Times may be set to any time within
a 7-day week. These settings are referred to as triggers. Multiple start or stop triggers may be set within a
single day, if desired. When a start trigger and a stop trigger are set to the same time, the stop trigger has
priority. The installer may adjust the DHW start triggers in the Start Time/ Stop Time parameter. This screen
shows the start trigger number, the day of the week, and the time of day.