A.O. Smith TC-049-R2 User Manual

A.O. SMITH SERVICE HANDBOOK

Residential Gas and Electric Water Heaters

Prepared by the Technical Training Department Asland City, Tennessee

The first portion of this Service Handbook addresses service issues

associated with Residential Gas Water Heaters that are atmospherically vented and use a thermocouple as their electrical source.

The second portion of this Handbook addresses service issues of Residential Electric Water Heaters having one or two heating elements and common wiring configurations for these models.

Printed in USA 0402 Part No. TC-049-R2 $15.00

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

TABLE OF CONTENTS

Page

Introduction

Terms......................................................... 1

Tools .......................................................... 2

Residential Gas Water Heaters

Guidelines.................................................. 3

Installation.................................................. 5

Operations and Servicing

Construction............................................... 6

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

Residential Electric Water Heaters

Installation................................................ 16

Standard Illustrations............................... 17

Guidelines................................................ 18

Elements.................................................. 19

Thermostat............................................... 20

Page Residential Electric continued

C-2 Circuit..........................................21

C-2 Sequence of Operation...............22

A-6 Circuit ..........................................23

A-6 Wiring Diagram ...........................24

A-7 .....................................................25

A-7 Wiring Diagram ...........................27

Certification and Approvals................29

Simultaneous Dual Elements ............30

C-2 Service ........................................31

C-2 Voltage Checks...........................32

C-2 Grounded Element Check ..........34

A-6 Service ........................................35

A-6 Element Test...............................35

A-6 Voltage Check.............................36

A-6 Grounded Element Test..............38

A-7 Service ........................................39

A-7 Element Test...............................40

A-7 Voltage Checks...........................41

A-7 Grounded Element Test..............44

Miscellaneous Information.................45

A.O. Smith Technical Bulletins 46

RESIDENTIAL GAS AND ELECTRIC 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.

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.hotwater.com 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.

. This handbook is intended for use by licensed

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

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

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

GENERAL SECTION

SERVICE GUIDELINES

MISCELLANEOUS INFORMATION

Draw efficiency

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

water heater. The higher the energy factor, the more efficient the water heater will be.

Recovery rate

might be that a water heater has a recovery rate of 30 gallons of water per hour at 80 degree F. (Fahrenheit) temperature rise.

Thermal efficiency

which enters the water. A percentage of the total BTU passes out through the vent piping.

is the quantity of hot water available to the consumer before the outlet water

is an indicator of the combined thermal efficiency and standby efficiency of a

is the amount of water that is heated to a set temperature, per hour. An example

is approximately the amount of generated BTU (British Thermal Units),

Temperature rise

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

water heat loss per hour is desired.

is the increase in the temperature from its coldest “inlet” water temperature to

– the water heater’s ability to contain heat in the tank. A minimum of tank

Water cannot Water expands Minerals and gases

(for all practical purposes) be compressed.

when it is heated.

will separate from water as temperature increases.

Formulas: BTU (British Thermal Unit)

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

One gallon

Pounds X .45359 = Kilogram Gallons X 3.7854 = Liters

% of Hot

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from Fahrenheit to Centigrade: (Degrees F – 32) times 5/9, or .556, equals degrees

of (120° F, 49°C) water weighs approximately 8.25 pounds.

= (Mixed Temp. – Cold) divided by (Hot Temp. – Cold)

is the heat required to raise 1 pound of water 1°F

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

General Section – continued

% Thermal Efficiency BTU Output GPH

= (BTU/H Input X % Eff.) divided by (Temp. Rise X 8.25)

One cubic foot One “therm” One cubic foot One gallon

= GPH X 8.25 X Temp. Rise X 1.0

of Natural Gas contains about 1000 BTU of heat.

is equal to 100,000 BTU

of Propane Gas contains about 2500 BTU of heat.

of Propane gas contains about 91,250 BTU of heat.

= (GPH X 8.25 X Temp. Rise X 1.0) divided by BTU/H Input

SERVICE HANDBOOK

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 to metal contact and rusting of the tank.

anode rod

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

limit

(to prevent water temperatures approaching the “steam” level).

will be installed within the tank. The hex-head plug end of the anode is visible on

glass lining

one thermostat

bonded to the steel. This prevents water

(to operate the heater) and

one high

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See Manual and Labels For Installation Clearances

Typical Model and Rating Plate Location

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

INSTALLATION OF RESIDENTIAL GAS WATER HEATER

Exhaust Vent to

Outside of Building

Union

Water

Shut Off

alve

Expansion Tank Pressurize to Equal Supply Water Pressure

Temperature And Pressure Relief Valve – Do Not Reuse Old Valve.

Maximum Gas Supply

13.8” w.c. or ½ PSI Minimum

4.5” w.c. –Natural Gas

11.0” w.c. Propane Gas

Air Is Drawn In For Combustion. Keep Area Clean And Free From Flammables And Flammable Vapors

Installation Must Follow Local Codes and Instruction Manual Guidelines

Temperature and pressure relief valve tube piped to within 6” of drain.

Thermostat – Recommending setting of 125°F.

Safety Pan – Piped to Drain

Drain

Inner and Outer Doors – Reinstall After Lighting Pilot.

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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.

Contro

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.

l: There is one control on this style of water heater. The control has a

▲(delta) Note: The word “Hot” may or may not be present on the control knob

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas – continued

Burner:

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.

The burner assembly consists of the main burner, main burner orifice, main burner gas

SERVICE HANDBOOK

AFTER HAVING CONFIRMED THAT THE WATER HEATER HAS BEEN INSTALLED

PER THE INSTALLATION MANUAL INSTRUCTIONS:

Normal Operation

Electrical:

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.

The Pilot Flame heats the end of a thermocouple. As the

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas – continued

Temperature:

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.

Two metal probes mounted

SERVICE HANDBOOK

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.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas - continued

Water Flow:

main forces cold water into the water heater. This pushes hot water out of the tank.

When a hot water faucet is opened, water pressure from the well tank or street

SERVICE HANDBOOK

Operation:

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.

A residential water heater is not a precise operating appliance. Because the water

Setting Approximate Temperature (°F) Time To Cause Injury

Hot (▲)

A 130° ± 10° 30 Seconds B 140° ± 10° 5 Seconds

C 150° ± 10° 1.5 Seconds

Very Hot 160° ± 10° Under 1 Second

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120° ± 10° 5 Minutes

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas - continued

SERVICE HANDBOOK

Service:

Air:

A gas burning appliance requires the oxygen contained in 12.5 cubic feet of air (at sea level)

for every 1000 BTU of heat that is generated. If your water heater has a BTU per hour input of 40,000 BTU then a minimum of 500 (40 times 12.5) cubic feet of clean air must be available. This oxygen will mix with the gas for a clean, blue flame in the burner chamber and provide dilution air for flue products.

(Enters Here)

Do not forget that your gas (or oil) furnace and gas clothes dryer also require a like amount of air.

When calculating air supply provisions, also consider the presence of whole house exhaust fans or other exhaust fans competing for the same air supply.

Air must be allowed to enter the heater chamber from the base of the heater and also enter the flue vent from below the draft hood. Do not block these areas with insulation blankets or obstructions lying around the base of the heater.

Lack of Oxygen:

dilution, the result will be:

• Pilot outage

• Yellow burner flame

• Sooting water heater

• Possible carbon monoxide

• Smell of burnt gas in the room

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If a sufficient supply of oxygen (air) is not available for combustion and

1,000

BTU Fuel

12.5

Cubic

Feet of

Air

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas – continued

The instruction manual gives guidelines under “Air Requirements” and “Unconfined “ or “Confined Space” sections. If you want to test for a lack of air:

1. Turn on every appliance and fan that exhausts air from the utility room and/or house. Make sure all windows and doors are closed, as well as chimney dampers.

2. Open a hot water faucet so that the main burner will ignite

3. Remove the outer door of the water heater – not the inner door

4. Monitor the flame characteristics for several minutes

If the flame begins to “yellow” open a door or window, to the outdoors, to see if additional air corrects this back to blue. If it does, the room needs more air supply. Perform draft test at draft hood of water heater with match or smoke source to verify.

Manifold Gas Pressure Test

Gas pressure checks are done with flowing gas.

Supply gas pressure

possible.

Pilot gas pressure

checks are taken ahead of the gas control and as close to the heater as

checks are taken by using fitting adapters to tap into the pilot gas tubing.

Manifold (main burner) gas pressure

of the control valve. Desired gas pressures will be noted on the gas valve label.

SERVICE HANDBOOK

Testing with

Gas

Pressure

Gauge

is measured using the Allen wrench tap on the bottom

Pilot Gas Pressure Test

If … … then

supply gas pressure is under desired pressure setting

supply gas pressure is over desired pressure

pilot gas pressure is more than +/- .3 inch W.C. from desired manifold gas pressure is more than +/- .3 inch W.C. from desired Additional considerations when pilot or main burner flames are too large or too small:

• Incorrect orifice

• Dirt in orifice or gas supply tubing

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• increase supply gas pressure regulator

setting and,

• increase supply gas piping size.

• add gas pressure regulator.

• reduce setting on existing regulator.

replace the control valve.

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas - continued

SERVICE HANDBOOK

Sooting causes

If … … then

the burner is clean but the chamber and/or flue are sooted the main burner, chamber and flue are sooted check the following:

check for lack of supply air.

•

incorrect orifice

•

excessive gas pressure

•

loose main burner

•

cross threaded orifice

•

gas control valve gas seepage

•

loose gas connection in burner assembly.

Electrical Testing

This type of water heater has its own electrical generating system.

When two dissimilar metals are joined together and this joint is heated, a small, electrical current will be produced. A thermocouple uses this science.

TO GROUND

Thermocouple output test Procedures/Conditions:

Meter set for DC millivolt testing Test from lower ECO (emergency cut off or energy cut off) solder joint to ground. Note: If pilot will not stay lit, manually hold the top knob down in the pilot position. This allows gas to flow to the pilot. Light the pilot and continue to hold this knob down while conducting the test.

If … … then

reading test of at least 13 MV is not present

reading test of at least 13 MV is present continue to next test.

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•

check that flame contacts end of thermocouple

•

replace thermocouple.

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas - continued Electrical Testing– continued

Millivolt dropout test Procedure:

Move meter probe to upper ECO solder joint and ground

through copper magnet winding and ECO (Emergency Cut Off)

SERVICE HANDBOOK

If … … then

reading of at least 10 MV is not present replace the control valve. reading of more than 10 MV is present but, gas to the pilot shuts off each time knob is released

Safety drop out test

– the safety gas shutoff

should interrupt gas through the valve when MV current drops to 1-3 MV.

replace the control valve.

Procedures:

Meter still connected to upper ECO solder joint and ground. Turn Top Knob to “off” position Millivolt output will decrease as thermocouple cools

TO GROUND

If… … then

internal safety does not activate between 1 and 3 MV (you will hear a “click” inside the valve) *internal safety does activate between 1 and 3 MV

*Note: A “click” sound should be heard from the valve as the main gas interrupter snaps up to the

“closed” position.

replace the control valve.

valve is within tolerance and will interrupt gas flow if pilot looses heat or ECO opens.

Condensation

Flue gas products contain moisture. If these flue gas products are cooled to their “dew point”, they become visible moisture – condensation.

Flue gas may become cooled by:

• Cold supply air temperatures

• Cool surfaces – generally, if tank water temperatures drop below 110°F, the flue pipe surface

and/or bottom tank head will be cool enough to cause condensation.

• Increased combustion efficiency – higher thermal efficiency means that an increased amount

of heat is transferring from the flue gas into the water. If you transfer (approximately) 87.5%, or more, the moisture in the flue gas will condense.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas – continued

SERVICE HANDBOOK

Condensation is a mild acid – it will corrode steel Condensation

• water dripping is heard (only) while the main burner is on,

• there is “water” around the heater just after the heater has been operating,

• there are small, black or red granules on the main burner or top of the heater or

• corroded jacket or vent piping is noted.

is usually noted when:

If … … then

any of the above conditions exist

•

raise the supply air temperature or

•

increase stored water temperature or

•

increase the size of the tank You would not wish to lower combustion efficiency – this would waste gas. Use materials (stainless steel, PVC etc.) that will not be affected by the condensation

Suggested Multiple Heater Water Piping Required For

Proper Operation of Top Connect Models

Installed in accordance with local codes.

TEMPERATURE/PRESSURE RELIEF VALVES

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas – continued

SERVICE HANDBOOK

Exhaust Venting Notes

Follow current National Fuel Gas Code requirements for proper installation.

“D” – Typically, same or larger diameter as Draft Hood outlet

“L” – Horizontal piping slopes upward ¼” per foot from heater to chimney or vertical vent Length of horizontal not more than 75% of “H”

“H” – Not less than 5 feet

Maximize vertical distance to first elbow

See the “Technical Bulletins Section “ of this manual for explanations of:

Water Hammer Mineral Buildup Aluminum Hydroxide Condensation Discolored Water Smelly Water Chlorination Process Lack of hot water Thermal Expansion Temperature and Pressure Relief Valve Operation

Parts Replacement

in the products. To order the current, correct replacement part for your model gas water heater, you must know the model number and (complete) serial number of your water heater. This information will be located on a black and white label, on the front of your water heater – this label will also display a star within a circle (the A.G.A. symbol). A sample might be: Model “PGCG-50 – 242” “Ser No. MB99-(numbers) – 242”.

– The parts on these models change often due to improvements/changes

To order parts, contact your local A.O. Smith Contractor or Distributor, phone AOS parts at 800-433-2545 or contact A. O. Smith on Web site “www.hotwater.com”

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

STANDARD RESIDENTIAL ELECTRIC WATER HEATERS

SOME MODELS MAY HAVE SIDE OR REAR CONNECTIONS

TEMPERATURE AND PRESSURE RELIEF VALVE OPENING MAY BE ON SIDE OR TOP OF HEATER. DO NOT REUSE OLD VALVE

SERVICE HANDBOOK

INSTALLATION

TO †FUSED ELECTRICAL SUPPLY (BREAKER BOX)

UNION

COLD WATER INLET LINE

SHUTOFF VALVE

HOT WATER TO FIXTURES

ELECTRICAL JUNCTION BOX ADJACENT CONDUIT ENTRANCE

RATING PLATE WITH MODEL AND SERIAL NUMBER

UNION

†FUSE SHOULD BE RATED AT AMPERAGE INDICATED ON RATING PLATE TIMES 125%

INSTALL THERMAL EXPANSION TANK AFTER SHUT OFF VALVE. PREPRESSURIZED TO EQUAL SUPPLY WATER PRESSURE

DRAIN LINE

ACCESS PANELS – WATER TEMPERATURE ADJUSTMENT IS BEHIND THESE PANELS. RECOMMENDED SETTING IS

6” AIR GAP

SEE MANUAL AND LABELS FOR INSTALLATION CLEARANCES

INSTALL DRAIN PAN TO PREVENT

INSTALLATION MUST FOLLOW LOCAL CODES AND INSTRUCTION MANUAL GUIDELINES.

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FLOOR

DRAIN VALVE

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

STANDARD RESIDENTIAL ELECTRIC WATER HEATERS

This portion of this manual applies to the Operation and Servicing of Residential Electric,

Tank Type, Water Heaters. The illustrations are for two element models but the

information also applies to single element models.

Multiple Heater Water Piping

Required for Proper Operation

of Top Connect Models

TEMPERATURE/PRESSURE RELIEF VALVES

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

STANDARD RESIDENTIAL ELECTRIC WATER HEATER SERVICE GUIDELINES

Construction

See “General Section” for features common to both gas and electric models. Miscellaneous: Amperage (Amps) (1 phase) = Watts divided by Volts Amperage (3 phase) = (Watts X .577) divided by Volts KW Required = (GPH X 8.25 X Temp. Rise X 1.0) divided by (3413) Ohms = Volts divided by Amperes One kilowatt is equal to 1000 watts One kilowatt is equal to 3,413 BTU Recovery Rate = (KW X 3413) divided by (Temp. Rise X 8.25) Rise (F°) = (KW X 3413) divided by (GPH X 8.25) Supply electrical fusing or breakers should be sized at least 125% of expected heater

amperage.

Water weighs 8.25 pounds per gallon at 120°F (49°C). % of Hot water = (Mixed temp. – Cold) divided by (Hot temp. – Cold)

Heating element(s)

This style water heater will have one or two electric, heating elements immersed in the tank. One element will always be located low in the tank; a second element is commonly located down about 1/3 of the tank height from the top of the tank. These elements will seldom be wired to operate at the same time. (If they operate at the same time, amperage draw doubles, wire gauge size increases, fuse size increases and little is gained in heat recovery.)

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