A.O. Smith TC-049R3 How to use

MODELS COVERED
Residential Gas Water Heaters that
are atmospherically vented and use a
thermocouple as their electrical source.
Residential Electric Water Heaters
having one or two heating elements
and common wiring configurations
for these models.
SERVICE HANDBOOK
Residential
Gas and Electric
Water Heaters
Part No. TC-049R3 • $15.00 • Printed in the U.S.A. • 0505

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
TABLE OF CONTENTS
Page
Introduction
Terms.................................................. 1
Tools ................................................... 2
Residential Gas Water Heaters
General Information ............................ 3
Installation........................................... 5
Operations and Servicing
Control................................................. 6
Burner ................................................. 7
Normal Operations .............................. 7
Temperature........................................ 8
Gas...................................................... 8
Water Flow.......................................... 9
Service .............................................. 10
Procedures and Conditions............... 11
Multiple Heater Piping....................... 14
Exhaust Venting Notes...................... 15
Flammable Vapor Ignition Design ……15
Lint, Dust & Oil Screen……………... 16
Flame Arrestor………………………...17
Thermal Cut Off Switch………….…...18
Pilot Burner Assembly……………..….19
Sealed Combustion Chamber………..20
Piezo Igniter…………………………….21
Miscellaneous ……………………….....22
Page
Residential Electric Water Heaters
Installation………………………………23
Standard Illustrations………………….24
Guidelines………………………………25
Elements………………………………..26
Thermostat….…………………….…..27
C-2 Circuit…………………………….28
C-2 Sequence of Operation…………29
A-6 Circuit……………………………..30
A-6 Sequence of Operation…….…..31
A-7 Circuit…………………………….32
A-7 Sequence of Operation…….……33
A-7 – wiring – Post 1995………...… 34
A-7 - Sequence of Operation ……….35
Certification and Approvals….……….36
Unbalanced 3 phase……………….…37
C-2 Ohms Check……………………...38
C-2 Ohms Check…………….………..39
C2 No Hot Water……………….……..40
C-2 Grounded Element Check………41
A-6 Ohms Check – No Hot Water…..42
A-6 No Hot Water Voltage Check…..43
A-6 Lack of Hot Water Voltage Ck….44
A-6 Grounded Element Test………...45
A-7 Service……………………………46
A-7 Ohms Test……………………….47
A-7 Voltage Checks………………….48
A-7 Lack of Hot ………………………49
A-7 Grounded Element Test………50-51
Miscellaneous and Ohms Table.……52
Technical Bulletins …………….. 53-66
RESIDENTIAL GAS AND ELECTRIC SERVICE HANDBOOK INTRODUCTION
This service handbook is designed to aid in servicing and troubleshooting A.O. Smith
Residential Gas and Electric 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.
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
1

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
The information contained in this handbook is designed to answer commonly faced
situations encountered in the operation of the Residential Gas and Electric 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 Center at 1-800-527-1953 or your local A.O. Smith
Water Products Company representative for further assistance. Additional information is also
available on the web site www.aosmithwaterheaters.com. This handbook is intended for use by
licensed plumbing professionals and reference should be made to the instructional manual
accompanying the product. This handbook contains supplemental information to the Residential
Gas and Electric instructional manual.
Qualifications
Tools Required:
For servicing gas models:
Cross top screw driver
3/8, 7/16, ¾ inch open end wrenches
3/16 inch Allen wrench
11/16 inch – 6 point – socket – for anode removal
set of marked drill bits
electrical multimeter
gas pressure gauge or monometer
water pressure gauge
thermometer
tubing cutter if pilot tube is to be replaced
hose – to drain tank
container – to measure gallons per minute flow
For servicing electric models:
1 1/16 inch – 6 point – socket (for anode removal)
1 ½ inch deep socket – to remove an element
electrical multimeter
water pressure gauge
thermometer
hose – to drain tank
container – to measure gallons per minute flow
Rev 1 adds Technical Bulletins
Rev 2 corrects illustration errors
Rev 3 adds FVIR (C3) Technology product information
2005 printing – revised cover
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
2

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
GENERAL SECTION
MISCELLANEOUS INFORMATION
Draw efficiency is the quantity of hot water available to the consumer before the outlet water
temperature decreases 25 degrees F. A 40 gallon water heater will typically provide 70% (28
gallons) of this “usable” hot water. The burner or elements are allowed to operate during this test.
Incoming, cold water mixes the remaining stored water below this 25 degree limitation.
Energy Factor is an indicator of the combined thermal efficiency and standby efficiency of a
water heater. The higher the energy factor, the more efficient the water heater will be.
Recovery rate is the amount of water that is heated to a set temperature, per hour. An example
might be that a water heater has a recovery rate of 30 gallons of water per hour at 80 degree F.
(Fahrenheit) temperature rise.
“R” Value is a measure of the resistance of a substance to heat flow.
Thermal efficiency is approximately the amount of generated BTU (British Thermal Units),
which enters the water. A percentage of the total BTU passes out through the vent piping.
Temperature rise is the increase in the temperature from its coldest “inlet” water temperature to
the desired hot (outlet) setting. Typically this is assumed to be 40 degrees entering water, 120
degrees desired stored water or 80 degrees “temperature rise.”
Standby efficiency – the water heater’s ability to contain heat in the tank. A minimum of tank
water heat loss per hour is desired.
Sample: temperature change = Btu/h loss/ square foot of tank surface
“R” value
Water cannot (for all practical purposes) be compressed.
Water expands when it is heated.
Water Hammer – is a concussion of moving water against the sides of a containing pipe or vessel
on a sudden stoppage of flow.
EX: 1/2 “copper pipe, 5GPM flow (7.2ft/sec.) – stop. Pressure rise of approximately 412 PSI.
3/4” copper pipe, 5GPM flow (3.3ft/sec) – stop. Pressure rise of approximately 188 PSI
Minerals and gases will separate from water as temperature increases.
Formulas:
BTU (British Thermal Unit) is the heat required to raise 1 pound of water 1F
1 BTU = 252 cal = 0.252 kcal
1 cal = 4.187 Joules
BTU X 1.055 = Kilo Joules
BTU divided by 3,413 = Kilowatts
To convert from Fahrenheit to Centigrade: (° F – 32) times 5/9, or .556, equals degrees C.
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
3

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
One gallon of (120F, 49C) water weighs approximately 8.25 pounds.
Pounds X .45359 = Kilogram
Gallons X 3.7854 = Liters
% of Hot = (Mixed Temp. – Cold) divided by (Hot Temp. – Cold)
General Section – continued
% Thermal Efficiency = (GPH X 8.25 X Temp. Rise X 1.0) divided by BTU/H Input
BTU Output = GPH X 8.25 X Temp. Rise X 1.0
GPH = (BTU/H Input X % Eff.) divided by (Temp. Rise X 8.25)
One cubic foot of Natural Gas contains about 1000 BTU of heat.
One “therm”is equal to 100,000 BTU
One cubic foot of Propane Gas contains about 2500 BTU of heat.
One gallon of Propane gas contains about 91,250 BTU of heat.
One pound of Propane gas contains about 21,600 BTU of heat.
One pound of gas pressure is equal to 27.7 inches water column pressure
Inches of Water Column X .036091 = PSI
Inches of Water Column X .073483 = Inches of Mercury (Hg.)
Centimeters = Inches X 2.54
MM (millimeters) =Inches X 25.4
Meters = Inches X .0254
Doubling the diameter of a pipe will increase its flow capacity (approximately) 5.3 times.
CONSTRUCTION: Tank is constructed of steel.
The inside of the tank is constructed of a glass lining bonded to the steel. This prevents water
to metal contact and rusting of the tank.
An anode rod will be installed within the tank. The hex-head plug end of the anode is visible on
the top of the water heater. This metal rod offers secondary protection of the tank against
corrosion where the application of glass is not possible (threaded tank openings). These areas
will have small areas of water to metal contact.
All water heaters will contain at least one thermostat (to operate the heater) and one high
limit (to prevent water temperatures approaching the “steam” level).
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
4

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
INSTALLATION OF RESIDENTIAL GAS WATER HEATER
Typical Model
and Rating
Plate Location
Union
Minimum
4.5” w.c. –Natural Gas
11.0” w.c. Propane Gas
Maximum Gas Supply
13.8” w.c. or ½ PSI
Air Is Drawn In For
Combustion. Keep
Area Clean And Free
From Flammables And
Flammable Vapors Inner and
Outer Doors –
Reinstall After
Lighting Pilot.
Drain
Safety Pan – Piped to
Drain
Thermostat –
Recommending
setting of 125F.
Temperature and
pressure relief valve
tube piped to within 6”
of drain.
Water
Shut Off
V
alve
Temperature And
Pressure Relief
Valve – Do Not
Reuse Old Valve.
Expansion Tank
Pressurize to Equal
Supply Water
Pressure
See Manual and
Labels For Installation
Clearances
Union
Exhaust Vent to
Outside of Building
Installation Must Follow Local Codes and Instruction Manual Guidelines
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
5

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
RESIDENTAL GAS WATER HEATER SERVICE
This portion of this manual applies to the Operations and Servicing of Residential Gas, Tank
Type, Water Heaters, which are vented atmospherically and use a thermocouple as their electrical
source.
Construction: See also “General” section of this
manual.
Control: There is one control on this style of water heater. The control has a main gas regulator,
pilot gas regulator, on-off-pilot knob, controls water temperature, has a temperature adjustment
knob, and a high water temperature limit safety.

(delta)
Note: The word “Hot”
may or may not be
present on the control
knob
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
6

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
Residential Gas – continued
Burner: The burner assembly consists of the main burner, main burner orifice, main burner gas
supply tube, pilot burner, pilot burner orifice, pilot burner gas supply tube and thermocouple.
The pilot burner remains on once it is manually lit. When incoming cold water activates the
thermostat, gas flows to the main burner. The pilot flame ignites this gas. The main flame burns
until the tank reaches set temperature then the thermostat interrupts this main gas flow.
AFTER HAVING CONFIRMED THAT THE WATER HEATER HAS BEEN INSTALLED
PER THE INSTALLATION MANUAL INSTRUCTIONS:
Normal Operation
Electrical: The Pilot Flame heats the end of a thermocouple. As the thermocouple gets hotter,
it generates a small (cannot be detected without an electrical meter) electrical current to the
bottom of the control valve. This current powers the electromagnet and holds open the safety
valve as long as the pilot flame is heating the thermocouple. DANGER! If the pilot is
extinguished, it can take up to 180 seconds for the thermocouple to cool sufficiently to close the
safety valve.
See also C3 technology product information beginning on page .
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
7

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
Residential Gas – continued
Temperature: Two metal probes mounted
onto the back of the control are immersed
inside the tank water. One probe (the
shorter) acts as a temperature high limit. If
water gets excessively hot, a sensor within
the probe opens, interrupts the small
electrical current to the gas valve, and gas
flow through the control is interrupted. If this
safety sensor opens, the entire control must
be replaced.
The longer probe contains a metal rod that
expands and contracts as water temperature
around the probe cools and heats. As the
rod expands, it pushes against a lever
actuated gas valve. If the regulator is
pushed sufficiently, gas flow is interrupted to
the main burner. Adjusting the temperature
dial changes the distance the rod must
expand or contract to open or close the gas
valve.
Gas: When you prepare to light the pilot,
you are instructed to turn the top
knob to the pilot position and depress
the knob. When the knob is
depressed gas will flow to the pilot
burner only. You then have to
(manually) ignite this pilot gas. When
the pilot is lit, the flame must heat the
thermocouple until it generates
sufficient electricity to the gas valve
to allow you to release the knob while
gas continues to flow to the pilot.
When the top knob is turned to the
“ON” position, gas is also available to
the main burner if the thermostat calls
for heat.
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
8

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
Residential Gas - continued
Water Flow: When a hot water faucet is opened, water pressure from the well tank or street
main forces cold water into the water heater. This pushes hot water out of the tank.
Operation: A residential water heater is not a precise operating appliance. Because the water
heater relies on the expansion and contraction of a metal rod, when the thermostat dial is set at
an indicated setting (“” is recommended as a starting setting. This is approximately 120 degrees
F.) the heater may shut off at 110 to 130F. The heater will consistently shut off at this same
temperature. For this same reason, water temperature may drop 15 - 25F, around the
temperature probe, before the main burner is activated. Keep in mind that hot water in the upper
part of the tank will probably be very near the “shut off” temperature of the control while incoming
cold water drops the water temperature around the thermostat probe. Also, short repeating
heating cycles caused by small hot water uses can cause temperatures at the point of use to
exceed the thermostat setting by up to 30° F.
Setting Approximate Temperature (°F) Time To Cause Injury
Hot (▲) 120° ± 10° 5 Minutes
A 130° ± 10° 30 Seconds
B 140° ± 10° 5 Seconds
C 150° ± 10° 1.5 Seconds
Very Hot 160° ± 10° Under 1 Second
A.O. Smith Water Products Company Technical Training Department
©2005 Ashland City, TN
9