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).

3
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.

5
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.

9
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