A.O. Smith BTH 120 Building instructions

Part No. TC-044R2
$15.00 Printed in the U.S.A. 3 00
This Service Handbook was prepared by:
The Training Department
Irving, Texas
BTH 120, 150, 199, 250
Service Handbook
Includes Parts List For
Series 960 through 967

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000©Training Department
1
BTH HANDBOOK
TABLE OF CONTENTS
PAGE
Introduction. .................................. 2
Installation
Clearances.................................. 3-4
Air Requirements ........................ 5-9
Contaminated Air ........................ 10
Flammable .................................. 10
Condensation .............................. 11
Venting ........................................ 12
Sequence of Operation
Mechanical .................................. 13
Information
Multiple Unit Piping...................... 14
Controls ...................................... 15-17
Troubleshooting
Pre-Service ................................. 18
Igniter Continuity Check ............... 18-19
Control Board Check ................... 20
Transformer ................................. 21-22
Control Board .............................. 22-23
Temperature ................................ 24
Blower ......................................... 25-26
PAGE
Troubleshooting - continued
Pressure Switch Continuity .......... 27-28
Voltage Test - Igniter .................... 29
250 Blower Test........................... 29
Gas Pressure Test ....................... 30
Tables
Component Part .......................... 31
Orifice Tables .............................. 31
Pressure Switches ...................... 32
Wiring Schematics
Natural and Propane Gas ............ 33
Service Aids. ................................. 34
General Questions & Answers..... 35
Error Codes................................... 36
Service Checklist .......................... 37
Parts Lists
966 & 967 Series ........................ 38-49
960 Series .................................. 50-53
962 Series .................................. 54-61

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000© Training Department
2
BTH HANDBOOK INTRODUCTION
This service handbook is designed to aid in servicing and troubleshooting A. O. Smith BTH 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 Water Products Company.
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 this product.
The information contained in this handbook is designed to answer commonly faced situations encoun-
tered in the operation of the BTH product line and is not meant to be all inclusive. If you are
experiencing a problem not covered in this handbook, please contact the A. O. Smith Technical
Information Department at 1-800-527-1953 or your local A. O. Smith Water Products company
representative for further assistance. This handbook is intended for use by licensed plumbing
professionals and reference should be made to the instruction manual accompanying the product.
This handbook contains supplemental information to the BTH instruction manual.
Qualifications: Installation or service of this water heater requires ability equivalent to that of a
licensed tradesman in the field involved. Plumbing, venting, gas supply and electrical testing skills are
required.
Tools Required:
• Phillips head screw driver
• Flat tip screw drivers
• Set of marked drill bits
• Electric multimeter tester
• Gas pressure gauge or manometer (gauge - AOS part number 8099-2)
• Water pressure gauge (AOS part number 4798)
• Draft gauge
• Thermometer (AOS part number 4870 - range 0 thru 220°F)
• 1/2 inch socket with extension for removal of the cleanout
• 1 1/8 inch socket for removal of the anode
• 1 inch socket for hot surface igniter removal
• Pipe wrench for union disconnect
*Note: Also, have a copy of the instruction manual for the model and series BTH
that you are servicing.
Revision 2 includes an added Multiple Venting statement on page 3 and a new Blower Motor Ohms
Resistance Table on page 25. The Pressure Switch Table on page 32 was expanded/revised.

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000©Training Department
3
Installation: This portion of the handbook will review often overlooked installation considerations, taking note
of necessary instruction requirements for the
BTH 120 - 250 / 966 and 967 Series. The instal-
lation manual covers most of these items in de-
tail. BTH heaters are approved for installation on
combustible flooring. Most can be installed in an
alcove with minimum clearances to combustibles
or non-combustibles of 0 inches from the sides
and rear, 0 inches from vent piping, and 1.5 inches
from the top cover. A 24 inch clearance for all
serviceable parts is recommended. Clearances
may vary between BTH models. See instruction
manual or the label on the heater for clearances
applicable to your specific model.
This illustrates the exterior clearances for these BTH units when installed as direct vent heaters.
BTH Model 120
BTH Model 150-199
BTH Model 250
Note: 24 inches between inlet and outlet is a minimum. Greater distance is
recommended. In colder climates increasing the 24" minimum to a maximum
practical distance, will reduce the possibility of frost over from side winds blow-
ing exhaust vapors to the air intake of the direct vent.

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000© Training Department
4
EXTERIOR CLEARANCES
Horizontal Vent (using room air for combustion)
EXTERIOR CLEARANCES
Direct Vent
CAUTION
DO NOT TERMINATE THE VENTING WHERE NOISE FROM THE EXHAUST OF INTAKE WILL BE OBJECTIONABLE.
THIS INCLUDES LOCATIONS CLOSE TO OR ACROSS FROM WINDOWS AND DOORS. AVOID ANCHORING THE
VENT AND INTAKE PIPES DIRECTLY TO FRAMED WALLS, FLOORS OR CEILINGS UNLESS RUBBER ISOLATION
PIPE HANGERS ARE USED. THIS PREVENTS ANY VIBRATIONS FROM BEING TRANSMITTED INTO THE LIVING
SPACES.
When multiple units are direct vented through a wall, all intake vent terminals must be no lower than the
highest exhaust vent terminal.
Regulator
Gas
Meter
3' Min.
3' Above Any Forced
Air Intake Within 10'
4' Minimum
4' Minimum
4' Minimum
Exhaust
3' Minimum
From
Inside Corner
Recommended
Vent Hood Must Be
Mounted 4' Minimum
Below Doors and Windows
Vent Hood Must Be
Mounted 4' Minimum
Below Windows
1' Above
Grade*
Vent Hood Must Be
Mounted 1' Minimum
Below Windows
*Recommended Clearance of 1' Above "Anticipated Snow Level" Where Applicable
Exhaust
Exhaust
Exhaust
Warning-
Vent Hood(s) May Be
Extremely Hot During
Operation
Regulator
Gas
Meter
3' Min.
1' Above
Grade*
3' Above Any Forced
Air Intake Within 10'
Vent Hood Must Be
Mounted 1' Away
Horizontally From Doors
and Windows
Vent Hood Must Be
Mounted 9" Minimum
Above Doors
and Windows
3' Minimum From
Inside Corner
Recommended
*Recommended Clearance of 1' Above "Anticipated Snow Level" Where Applicable
Exhaust
Exhaust
Exhaust
Exhaust
Intake
Intake
Intake
Intake
Air
intake
(optional)
Intake Air Must Be
Mounted 1' Minimum
Below Windows
Exhaust 4"
Minimum
Warning-
Vent Hood(s) May Be
Extremely Hot During
Operation

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000©Training Department
5
MINIMUM AIR FOR COMBUSTION
10 CUBIC FEET OF AIR PER 1,000 BTU
Stoichiometric or theoretical complete combustion requires 10 cubic feet of air per 1000 BTUH input of the gas
input. The National Fuel Gas Code also recommends an additional 2.5 cu.ft. of "excess air". This
12.5 cu.ft. minimum supply air per 100 BTUH input applies to natural and propane gas models.
The National Fuel Code also specifies minimum make-up air opening sizes for various building installations.
(Ref: NFPA 54, ANSI Z223.1, sec 5.3).
MAKE-UP AIR
DIRECT VENT INSTALLATION
This model is approved for direct venting either horizontally or vertically or conventional venting horizontal or
vertical. Direct venting avoids using room air for combustion and eliminates the need for additional air
intake ducts. The direct vent installation may have up to 50 equivalent feet of exhaust and 50 equivalent feet
of air intake piping
1,000
BTU
10 CU.
FT.
COMB.
AIR
2.5 CU. FT.
EXCESS
AIR
+

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000© Training Department
6
MAKE-UP AIR
DIRECT COMMUNICATION
A fresh supply of make-up air for combustion can be supplied to the heater through make-up air ducts, which
directly communicate with the out of doors. 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 shall have a free area of not
less than 1 square inch per 4000 BTUH of the total input of all appliances within the enclosure.
The lower opening is primarily providing combustion air. The upper opening is providing vent dilution air and
acts as a relief opening for flue gases should the vent become obstructed or a down draft condition occur.
Additionally, when the heater is installed in a confined space and communicating with the outdoor air, one
permanent opening, commencing within 12 inches (30 cm.) of the top of the enclosure, shall 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 shall directly communicate with the outdoors
and shall communicate through a vertical or horizontal duct to the outdoors or spaces (crawl or attic) that
freely communicate with the outdoors, and shall have a minimum free area of:
a. 1 sq. in. per 3000 BTU per hr (7 cm2 per kW) of the total input of all equipment located in the
enclosure, and
b. Not less then the sum of the areas of all vent connectors in the confined space.

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000©Training Department
7
MAKE-UP AIR
VERTICAL DUCTS
Often it is more practical to install vertical make-up air ducts to the out doors. Again, two openings are required
- within 12 inches (30 cm.) of the top of the enclosure and one within 12 inches (30 cm.) of the bottom of the
enclosure. Each opening shall have a free area of not less than 1 square inch per 4000 BTUH of the total input
of all appliances within the enclosure.

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000© Training Department
8
MAKE-UP AIR
HORIZONTAL DUCTS
When the heater is installed in an interior room with no roof access for vertical ducts, horizontal make-up
ducts should be installed. When using horizontal ducts, two openings are required - within
12 inches (30 cm.) of the top of the enclosure and one within 12 inches (30 cm.) of the bottom of the enclo-
sure. Each opening shall have a free area of not less than 1 square inch per 2000 BTUH of the total input of all
appliances within the enclosure.
Fresh AirFresh Air
Fresh AirFresh Air
Fresh Air
Fresh AirFresh Air
Fresh AirFresh Air
Fresh Air

A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000©Training Department
9
INSUFFICIENT MAKE-UP AIR
BACKDRAFT
Insufficient make-up air is a major cause of combustion problems. One common example is in a restaurant
installation where exhaust vent equipment was not considered in sizing make-up air requirements. This may
result in air being backdrafted by the restaurant exhaust equipment through the heater causing flue gas spill-
age, flame roll out, improper combustion, inconsistent pilot operation, and/or erratic heater shutdown.
A possible solution to this situation would be to use a BTH with direct venting.
A less common service issue associated with a backdraft or negative pressure room would be the opening or
closing of air pressure switches. This may result in erratic or no heater operation.