A.O. Smith Master-Fit 100 Series How to use

500 Tennessee Waltz Parkway
Ashland City, TN 37015
PRINTED IN THE U.S.A. 0713 317923-001
SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE TECHNICIAN
Service Handbook
COMMERCIAL GAS WATER HEATERS
FOR MODELS:
BTN 120 thru 400(A) Series 100 - 108
BTR 151 & 201 Series 100 & 101
INSTALLATION CONSIDERATIONS - PRE SERVICE CHECKS -
CONSTRUCTION - OPERATION & SERVICE - TROUBLESHOOTING

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Servicing should only be performed by a Qualied Service Technician
TABLE OF CONTENTS
INTRODUCTION ......................................................................2
QUALIFICATIONS .....................................................................2
TOOLS REQUIRED ....................................................................3
INSTALLATION CONSIDERATIONS .......................................................4
GAS AND ELECTRICAL CHARACTERISTICS ...............................................4
GAS PRESSURE – REQUIREMENTS .....................................................4
MINIMUM CLEARANCES ...............................................................8
EXTERIOR CLEARANCES ..............................................................9
GAS VALVE .........................................................................10
GAS VALVE .........................................................................11
VENTING TABLES FOR CATEGORY 1 – TYPE B GAS VENT .................................12
DRAFT PROVING PRESSURE SWITCH – SETTINGS .......................................14
THERMOSTAT AND IGNITION CONTROL BOARD VIEW .....................................15
WHITE RODGERS INTEGRATED CONTROL – THERMOSTAT ................................16
WHITE RODGERS IGNITION CONTROL BOARD ...........................................17
GAS CONTROL VALVE/ BURNER AREA VIEW .............................................18
BTN/ BTR 151, 201 – ELECTRICAL SEQUENCE............................................19
OPERATING SEQUENCE – FLOW CHART ................................................20
HEATER CONTROL BOARD DIAGNOSTIC LED INTERPRETATION AND TROUBLESHOOTING .....21
IGNITION CONTROL BOARD DIAGNOSTIC LED INTERPRETATION AND TROUBLESHOOTING ....22
TEST 2 - POLARITY CHECK............................................................23
TEST 3 –CONTINUITY CHECK OF HIGH LIMIT (ECO) ......................................24
TEST 4 –UPPER TEMPERATURE PROBE CONTINUITY CHECK..............................25
TEST 5 –CALLING FOR HEAT – NO INDUCER OPERATION .................................26
TEST 6 –INDUCER ON – NO IGNITION ..................................................27
TEST 7 –INDUCER ON – PROVER SWITCH AND LOW GAS SWITCH CLOSED. NO IGNITER
OPERATION.........................................................................28
TEST 8 –IGNITER HEATS – NO MAIN BURNER ...........................................29
TEST 9 –IGNITER HEATS – NO MAIN BURNER ...........................................30
TEST 10 –MAIN BURNER IGNITION FOR LESS THAN 5 SECONDS ...........................31
TEST 11 –WATER HEATER SHUTTING OFF BELOW SETTING ...............................32
DISPLAY LIGHTS ON INTEGRATED HEATER CONTROL.....................................33
WIRING DIAGRAM ...................................................................34
NOTES .............................................................................35
NOTES .............................................................................36
NOTES .............................................................................37

2Servicing should only be performed by a Qualied Service Technician
INTRODUCTION
The service handbook is designed to aid in servicing and troubleshooting A. O. Smith BTN and BTR
151/201 commercial water heaters in the field. No duplication or reproduction of this book may be made
without the express written authorization of the A. O. Smith Corporation.
The following text and illustrations will provide you with a step by step procedure to verify proper installation,
operation, and troubleshooting procedures. Additional quick reference data is included to assist you in
servicing these products.
The information contained in this handbook is designed to answer commonly faced situations encountered
in the operation of this product line and is not meant to be all inclusive. If you are experiencing a problem not
covered in this handbook, please contact A. O. Smith Technical Information at 1-800-527-1953, by email at
[e-mail], or your local A. O. Smith Corporation representative for further assistance. Our website
at: http://www.hotwater.com is also a resource for installation and service information. This handbook is
intended for use by licensed plumbing professionals and reference should be made to the installation manual
accompanying the product. This handbook contains supplemental information to the product’s installation
and operation manual.
QUALIFICATIONS
“Qualified Service Technician" or "Qualified 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 Sec. 3.3.85: “Qualified Agency” - “Any individual, firm, corporation or company that either
in person or through a representative is engaged in and is responsible for (1) the installation, testing or
replacement of gas piping or (2) 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 of this water heater requires ability equivalent to that of a Qualified Service Technician in the field
involved. Installation skills such as plumbing, air supply, venting, gas supply, electrical supply are required in
addition to electrical testing skills. Some products may require combustion testing equipment and certification.
If you do not possess these skills or do not have the proper tools you should not attempt to service this water
heater.
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 manual. If you do not understand the instructions given in this manual do not attempt to perform any
procedures outlined in this manual.
SERVICE REMINDER
When performing any troubleshooting step outlined in this 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.

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Servicing should only be performed by a Qualied Service Technician
TOOLS REQUIRED
• Electrical multimeter capable of measuring continuity/ ohms, ac & dc volts, amperes, microamperes,
millivolts, and frequency (hz)
• UEi Model DL289 or equivalent
• Digital manometer + 60" W. C., resolution 0.01" increments
Note: A digital manometer is required for testing pressure switches and can replace a gas pressure
gauge, draft gauge or slack tube manometer for checking gas pressure.
• UEi model EM200 or equivalent
• Water pressure gauge w/lazy hand and hose bibb connection
• Thermometer
• 1-1/16 Inch socket with extension for anode replacement
• Phillips head screwdriver
• Set of numbered drill bits
• Standard screwdrivers
• 3/8, 7/16, 1/2 and 9/16 inch open end wrench
DIGITAL MANOMETER DIGITAL MULTIMETER
WATER PRESSURE
TEST GAUGE W/LAZY
HAND AND HOSE BIBB
CONNECTION

4Servicing should only be performed by a Qualied Service Technician
INSTALLATION CONSIDERATIONS
GAS AND ELECTRICAL CHARACTERISTICS
Models Gas Type
Gas Supply Pressure Gas
Manifold/
Pressure
Volts/Hz Amperes
Minimum Maximum
All Models Natural 5.2" W.C. (1.29 kPa) 14.0" W.C. (3.48 kPa) 120/60 120/60 < 5
All models require a minimum gas supply pressure of 5.2” W.C. The minimum supply pressure is measured
while gas is flowing (dynamic pressure). The supply pressure (dynamic) should never fall below 5.2” W.C.
The supply pressure should be measured with all gas fired appliances connected to the common main firing
at full capacity. If the supply pressure drops more than 1.5” W.C. as gas begins to flow to the water heater
then the supply gas system including the gas line and/or the gas regulator may be restricted or undersized.
The gas valve on all models has a maximum gas supply pressure limit of 14" W.C. The maximum supply
pressure is measured while gas is not flowing (static pressure).
GAS PRESSURE – REQUIREMENTS
Main line gas pressure to the water heater for natural gas should be between a maximum of 14" W.C.
(3.48 kPa) static pressure and a minimum of 5.2" W.C. (1.29 kPa) dynamic pressure for Natural Gas.
A supply gas pressure regulator (service regulator) must be installed on the gas supply line no
closer than 3 feet (1 meter) and no farther than 8 feet (2.4 meters) of equivalent length from the
water heater's inlet connection.
1. Check gas line pressure with a manometer.
2. Cycle the burner on and off several times to check its operation.
3. Check the operation of the limit and operating controls.
4. Check the vent system seams and joints and ensure that there is no discharge of flue products into
the room.
5. Check the input rate.
Supply gas pressure shall be measured while the water heater is not firing (static pressure) and while the
water heater is firing at full capacity (dynamic pressure). If the supply gas pressure to the water heater is not
between the required minimum and maximum values given in table above, adjust the supply gas regulator
as necessary. Adjust the supply gas regulator(s) per the regulator manufacturer’s instructions to achieve the
required “static” and “dynamic” supply gas pressure.
MULTIPLE APPLIANCE INSTALLATIONS:
In multiple water heater installations or in installations where the installed water heater(s) share a common
gas supply main with other gas fired appliances; the supply gas pressures shall be measured at each water
heater with all gas fired appliances connected to a common main firing at full capacity.
In multiple water heater installations the supply gas line regulators shall be adjusted to provide gas pressure
to each water heater within the minimum and maximum supply pressure requirements listed in table above
with all gas fired appliances connected to a common gas main firing at full capacity.
Note: A pressure drop of more than 1.5” W. C. (0.37 kPa) when the main burner ignites is an indication of
an inadequate supply of gas and can lead to ignition failure, rough starts and/or rough operation. If a
drop of more than 1.5” W. C. (0.37 kPa) in supply gas pressure occurs when the main burner ignites,
ensure the supply gas lines and regulator(s) are properly sized and installed.

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Servicing should only be performed by a Qualied Service Technician
AIR SUPPLY:
Stoichiometric or theoretical complete combustion requires 10 cubic feet of air per 1,000 BTU of gas supplied.
The National Fuel Gas Code also recommends an additional 2.5 cubic feet of “excess” air. For information
on minimum make-up air opening sizes for various building installations, refer to the National Fuel Gas Code
NFPA 54/ANSI Z223.1.
INSUFFICIENT MAKE-UP AIR, NEGATIVE AIR PRESSURE AND DOWNDRAFTS:
A lack of combustion and ventilation air can create a negative ambient air pressure in the installed space. The
vent system on one or more gas fired appliances can experience down drafts due to the outdoor air pressure
being greater than the ambient air pressure in the installed space. Where multiple gas fired appliances are
installed, one or more gas fired appliances can “pull air” through the vent system(s) of other appliances
installed nearby.
One common example is in a restaurant installation where exhaust vent equipment was not considered in
sizing make-up requirements. This condition may result in air being back drafted by the restaurant exhaust
equipment through the heater causing the draft proving switch to open and/or erratic heater shutdown.
• Down drafts can cause flue gases to spill into the installed space.
Downdraft Caused by Kitchen Vent Hood

6Servicing should only be performed by a Qualied Service Technician
MAKE-UP AIR –DIRECT COMMUNICATION WITH OUTDOORS:
A fresh supply of make-up air for combustion can be supplied to the water heater through make-up air ducts,
which directly communicate with the outdoors. (Not Direct Vent.)
Two openings are required: one within 12 inches of the top of the enclosure and one within 12 inches
of the bottom of the enclosure. Each opening must have a free area of not less than 1 square inch per
4,000 BTU/Hr of the total input of all appliances within the enclosure. The lower opening primarily provides
combustion air. The upper opening provides vent dilution air and acts as a relief opening for flue gases
should the vent become obstructed or a downdraft condition occur.
Additionally, when the water heater is installed in a confined space and communicating with the outdoor air,
one permanent opening, beginning within 12 inches (30 cm) of the top of the enclosure, must be permitted
where the equipment has clearances of at least 1 inch (2.5 cm) from the sides and back, and 6 inches
(16 cm) from the front of the appliance. The opening must directly communicate with the outdoors and
must communicate through a vertical or horizontal duct to the outdoors or spaces (crawl or attic) that freely
communicate with the outdoors, and must have a minimum free area of a) 1 square inch per 3,000 BTU/Hr
(7cm2per kW) of the total input of all equipment located in the enclosure and b) not less than the sum of the
areas of all vent connectors in the confined space.
CONTAMINATED AIR:
Corrosion of the flue ways and vent system may occur if air for combustion contains certain chemical vapors.
Such corrosion may result in failure and risk of asphyxiation.
Combustion air that is contaminated can greatly diminish the life span of the water heater and water heater
components such as hot surface 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.
Do not store products of this sort near the water heater. Air which is brought in contact with the water
heater should not contain any of these chemicals. If necessary, uncontaminated air should be obtained from
remote or outdoor sources. The limited warranty is voided when failure of water heater is due to a corrosive
atmosphere. (See limited warranty for complete terms and conditions).

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Servicing should only be performed by a Qualied Service Technician
AIR REQUIREMENTS:
For safe operation an adequate supply of fresh uncontaminated air for combustion and ventilation must be
provided.An insufficient supply of air can cause recirculation of combustion products resulting in contamination
that may be hazardous to life. Such a condition often will result in a yellow, luminous burner flame, causing
sooting of the combustion chamber, burners and flue tubes and creates a risk of asphyxiation.
Do not install the water heater in a confined space unless an adequate supply of air for combustion and
ventilation is brought in to that space using the methods described in the Confined Space section of the
Instruction Manual.
Never obstruct the flow of ventilation air. If you have any doubts or questions at all, call your gas supplier.
Failure to provide the proper amount of combustion air can result in a fire or explosion and cause property
damage, serious bodily injury or death.
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.
CONTAMINATED AIR:
Corrosion of the flue ways and vent system may occur if air for combustion contains certain chemical vapors.
Such corrosion may result in failure and risk of asphyxiation.
Combustion air that is contaminated can greatly diminish the life span of the water heater and water heater
components such as hot surface 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.
Do not store products of this sort near the water heater. Air which is brought in contact with the water
heater should not contain any of these chemicals. If necessary, uncontaminated air should be obtained from
remote or outdoor sources. The limited warranty is voided when failure of water heater is due to a corrosive
atmosphere. (See limited warranty for complete terms and conditions).
POWER SUPPLY:
The water heaters covered in this manual require a 120 VAC, 1Ø (single phase), 60Hz, 15 amp power
supply and must also be electrically grounded in accordance with local codes or, in the absence of local
codes, with the National Electrical Code, ANSI/ NFPA 70 or the Canadian Electrical Code, CSA C22.1.

8Servicing should only be performed by a Qualied Service Technician
MINIMUM CLEARANCES
This water heater is approved for installation on combustible flooring in an alcove with minimum clearance
from combustion construction as indicated in below Figure and Table.
In all installations the minimum combustible clearances from vent piping shall be 6” (15.2 cm). Vent piping
passing through a combustible wall or ceiling must be a continuous run (no joints) and retain 6” (15.2 cm)
clearance unless an approved reducing thimble is used.
A service clearance of 24” (61 cm) should be maintained from serviceable parts, such as Temperature-
pressure relief valves, baffles, digital thermostats, cleanout openings or drain valves.
The units are approved for installation with side, rear and ceiling clearances as indicated below:
MINIMUM CLEARANCES TO COMBUSTIBLE OR NON-COMBUSTIBLE CONSTRUCTION:
MODELS "A" RIGHT SIDE "B" LEFT SIDE "C" BACK "D" CEILING
BTN - 120 thru 275/A 2" 2" 2" 12"
BTN - 310/A and 366/A 6" 6" 6" 12"
BTN - 400 3" 3" 3" 12"
BTR 151 & 201 2" 2" 2" 12"
A, B, and C clearances to non-combustibles is “0” inches except for the BTN - 199C which is 2" and the BTN
- 310/A which is 3". The 12" ceiling clearance remains unchanged for all models.