A.O. Smith TC-049R3 User Manual

SERVICE HANDBOOK

Residential

Gas and Electric

Water Heaters

M O D E L S C O V E R E D

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.

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.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

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.

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 Rev 3 adds FVIR (C3) Technology product information 2005 printing – revised cover

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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

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.”

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

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: “R” value

temperature change = Btu/h loss/ square foot of tank surface

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)

1 BTU = 252 cal = 0.252 kcal 1 cal = 4.187 Joules BTU X 1.055 = Kilo Joules

BTU divided by 3,413 = Kilowatts

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

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

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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 to metal contact and rusting of the tank.

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

limit

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

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glass lining bonded to the steel. This prevents water

one thermostat (to operate the heater) and one high

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

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 main gas regulator,

(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

SERVICE HANDBOOK

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:

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 thermocouple gets hotter,

See also C3 technology product information beginning on page .

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas – continued

SERVICE HANDBOOK

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.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas - continued

SERVICE HANDBOOK

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 (▲)

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.

1,000

BTU Fuel

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

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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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.

SERVICE HANDBOOK

Testing with

Gas

Pressure

Gauge

Pilot Gas Pressure Test

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

possible.

Pilot gas pressure checks are taken by using fitting adapters to tap into the pilot gas tubing. Manifold (main burner) gas pressure is measured using the Allen wrench tap on the bottom

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

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  check that flame contacts end of

thermocouple

 replace thermocouple.

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

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

Residential Gas - continued Electrical Testing– continued

SERVICE HANDBOOK

Millivolt dropout test through copper magnet winding and ECO (Emergency Cut Off) Procedure: Move meter probe to upper ECO solder joint and ground

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

replace the control valve.

Safety drop out test – the safety gas shutoff

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

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

FLAMMABLE VAPOR IGNITION RESISTANT DESIGN

This section will address the changes brought about by the introduction of FVIR compliant products. Other than items mentioned here, the construction, installation, and service will remain the same as discussed in the primary handbook.

The FVIR acronym stands for "Flammable Vapor Ignition Resistant." The AO Smith products are based on "Corderite Combustion Containment" known as “C3 Technology™” . The C3 Technology design features a sealed (from non designated air intake openings) combustion chamber and a "flame arrestor" component.

This class of residential gas water heaters meet the new ANSI standards and testing protocols (ANSI Z21.10.1) established to deal with the accidental or unintended ignition of flammable vapors, such as those emitted by gasoline. Virtually all gas-fired, atmospherically vented, residential water heaters manufactured in the United States with BTU ratings of 75,000 or less are required to meet this new ANSI standard effective July 1,2003. The current implementation schedule for C3 TECHNOLOGY compliant residential gas-fired products is shown in the following table. These dates are subject to change.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

IMPLEMENTATION CATEGORY

Phase I July 1, 2003

Phase II January 1, 2005

Phase III July 1, 2005 All other gas-fired models with inputs of 75,000 BTU or less.

This supplement addresses the July1, 2003 compliant products.

In addition to the standard water heater design discussed in the main service handbook, the C3 Technology design also includes:

 A LDO (Lint Dust and Oil) screen over the combustion air intake  A Flame Arrestor  A combustion chamber Thermal Cut Off (TCO) limit

An additional tool for these products might be a vacuum cleaner with both blowing and vacuuming capabilities. Also include the long, narrow crevasse accessory.

ANTICIPATED INTRODUCTION

CLASS OF PRODUCTS INCLUDED IN THIS CATEGORY

30, 40, and 50 gallon atmospheric vented. (Manufactured housing models are excluded.)

30, 40, and 50 gallon power-vented models. (Manufactured housing models are excluded.)

LDO SCREEN (LINT, DUST, OIL) SCREEN(S)

An easy to clean screen designed to minimize lint, dust and oil based contaminants from being drawn into the “Flame Arrestor” along with make up – combustion - air. There may be one or two of these screens. The LDO screen must be installed with the arrows on the right and left side facing up to function properly. (The arrows are located on two mounting tabs on each side of the screen).

Service:

Inspect the LDO screen(s) regularly. Clean or wash as necessary.

Pulling the tab located in the middle of the screen will remove the screen. Reinstall the clean screen by inserting the end tabs into the jack with the arrows pointing up.

Possible Service issues associated with a blocked screen:

 Poor combustion – yellow flame, possible sooting  Pilot outage resulting from a lack of oxygen  Pilot outage resulting from to increased combustion chamber temperature below the main burner.

This may open the automatic reset, thermal cut off switch (TCO).

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

FLAME ARRESTOR

Made from Corderite, a fireproof ceramic material, the flame arrestor is built into the base of the water heater. Combustion air is drawn in through the LDO screen (s). After entering the bottom area of the water heater, this air passes up through the small ports of the flame arrestor and into the combustion chamber.

In the event flammable vapors are introduced accidentally into the combustion chamber, the flame arrestor is designed so any flames burn off the top surface of the arrestor and cannot escape down through the arrestor. The arrestor works somewhat like a check valve.

Service:

Inspect the bottom ports of the flame arrestor by removing the LDO screen (s) and using a mirror and flashlight. Clean the ports if necessary by vacuuming the bottom of the arrestor.

Inspect the top of the flame arrestor by removing the inner door and burner assembly. Lift the heat shield located on the bottom of the chamber. Inspect with the mirror and flashlight. Vacuum or blow down any blocking material. If you blow down through the ports, be certain to also vacuum below the arrestor.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

If there has been a flammable vapor ignition, a qualified service agent needs to inspect the arrestor for cracks. The arrestor is not a replaceable part – the heater would need to be replaced.

Possible service issues associated with the flame arrestor.

 Poor combustion – yellow flame, sooting, possible carbon monoxide production.  Pilot outage due to lack of oxygen. Continued pilot outage or finding that the LDO screen(s) is

heavily blocked would warrant inspection of the flame arrestor.

 Pilot outage due to increased combustion chamber temperatures below the main burner. This may

open the automatic reset, thermal cut off switch (TCO).

 The flame arrestor having contained a flammable vapor ignition. The TCO will open and the

chamber and arrestor should be inspected by a qualified service agent.

SERVICE HANDBOOK

COMBUSTION CHAMBER TEMPERATURE SENSOR

The C3 Technology water heaters will come equipped with a thermal cutoff (TCO) device that is integral with the thermocouple. Temperature cutoff points range from 160°C to 200°C depending on model. The TCO is an automatic reset thermal switch. When activated it will open the thermocouple circuit and shut off the main and pilot burner gas flow. The pilot would have to be relit after the TCO has had sufficient time to cool down (sensor is below 120 degrees F).

The TCO performs two primary functions:

SERVICE:

 In the event of flammable vapor ignition inside the combustion chamber, it senses the

corresponding increase in temperature and shuts off gas flow to the main and pilot burners.

If excessive temperatures inside the combustion chamber indicate poor combustion due to



a clogged LDO screen or inadequate air for combustion, the TCO will shut off gas flow to

the main and pilot burners.

There is no routine service associated with the TCO. The standard thermocouple millivolt output checks described in this service handbook still apply. Millivolt readings indicate that the TCO is closed. An open TCO (within a cool chamber) would indicate that the assembly must be replaced.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

The TCO is an integral part of the thermocouple and not replaceable as a separate item. A pilot burner assembly must be reinstalled. On repeated calls of no hot water or pilot outage, a clogged/dirty LDO screen might be the cause and should be checked. Keep in mind this TCO will shut off the pilot and main burner when activated.

With the different cutoff temperature set-points of TCO devices for different model water heaters, it is important that the correct part is used when replacement of the pilot burner assembly is necessary.

Possible service issues associated with the Thermal Cut Off switch being opened:

 Pilot outage due to increased combustion chamber temperatures below the main burner. This may

open the automatic reset, thermal cut off switch (TCO).

SERVICE HANDBOOK

 The flame arrestor having contained a flammable vapor ignition. The TCO will open and the

chamber and arrestor should be inspected by a qualified service agent.

ONE PIECE PILOT BURNER ASSEMBLY

C3 Technology models feature a "one piece" pilot burner assembly. This assembly will be covered under a minimum 6 year parts warranty on all C3 Technology models, 10 years on premium models.

There are five main components that make up this pilot assembly:

1. Thermocouple with integral Thermal Cut Off switch (TCO).

2. Pilot burner w/orifice and tubing

3. Piezo igniter cable

4. Pilot assembly seal/grommet (orange).

5. An inner door gasket (white) will also be included.

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RESIDENTIAL GAS AND ELECTRIC WATER HEATER

SERVICE HANDBOOK

To replace a pilot assembly:

1. Turn off the gas supply

2. Disconnect the piezo cable from the piezo button (connection near gas control valve).

3. Disconnect the pilot tubing, thermocouple and main burner tube from the bottom of the gas control valve.

4. Remove (2) 3/8 inch nuts securing the inner door.

5. Remove the entire burner assembly.

6. Remove screw securing pilot burner assemble to pilot mounting bracket.

7. Remove pilot assemble - with orange gasket – from the back side of the inner door.

8. Reinsert new pilot assembly into back side of inner door. Wetting the orange gasket may help in securing the gasket into place.

9. Reattach the new pilot assembly to the pilot mounting bracket.

10. Inspect/replace the white, inner door gasket before making the connections to the bottom of the gas control valve.

11. Reattach the piezo cable to the piezo button.

12. Remount the inner door.

13. Follow the pilot lighting instructions including gas and gasket leak checks.

14. Install the outer door.

SEALED COMBUSTION CHAMBER

The combustion chamber is factory sealed around the flame arrestor and the upper and lower perimeter of the chamber. Access for service is provided through an inner door as with current product. However, this inner door is now sealed with; a door gasket, a pilot assembly grommet type seal, and a main burner tube boot/sleeve type seal.

The three seals on the inner door should be checked every time any service is performed. The sight glass should be checked to insure it is not damaged or missing. The pilot tube and thermocouple routing should be straight (not bent at an angle close to the surface of the seal) as it passes through the pilot assembly seal.

A.O. Smith Water Products Company Technical Training Department

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