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

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

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

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

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

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

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

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

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

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

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

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 Air

Fresh AirFresh Air

Fresh Air

A. O. Smith Water Products Company Service Handbook

Irving, Texas 2000©Training Department

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.

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