A O Smith 120 Trough 500 Handbook NAME

120trough500 0c48242d-3c83-4152-90f5-c2442a241ec6 A.O. Smith Water Heater 120 trough 500 User Guide |

2015-01-05

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BTR TANK TYPE HEATERS
SERVICE HANDBOOK
BTR HANDBOOK
TABLE OF CONTENTS

PAGE

PAGE
Troubleshooting (continued)

Introduction

1-2

Installation
Clearances
Air Requirements
Contaminated Air
Flammable
Gas Pressure
Gas Valve
Venting

3-4
5-9
10
10
11
12
13-15

Sequence of Operation
Mechanical
Electrical
Troubleshooting
Transformer
High Limit
Damper (on Standby)
PC Board
Thermostat
Damper (call for heat)
Effikal Damper
Effikal Harness Test
Normal Operation

Troubleshooting the Efflkal
Wire Harness Test
IID Module
Pilot Spark
Pilot Valve
Main Burner Test
Flame Rectification
IID Module
Main Gas Valve 40-41

16
17-18

19
20-21
22
22-23
24
25-26
27
28
28-29

30-31
32
33
34
35-36
37
38
39

Wiring Schematics
Natural and Propane Gas

Service Charts

General Questions & Answers

Parts List

45-50

Component Part Information

Service Check List

52-53

Comments

BTR WORKBOOK INTRODUCTION
This service handbook is designed to aid in servicing and troubleshooting A.O. Smith BTR 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 common questions encountered in the
operation of the BTR 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 1-800-5271953 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
installation manual accompanying the product. This handbook contains supplemental information to the BTR
installation and operation manual.

A.O. Smith Water Products
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SERVICE HANDBOOK
Qualifications: Installation or service of this water heater requires ability equivalent to
that of a licensed tradesman in the field involved. Plumbing, air supply, venting, gas
supply and electrical testing skills are required.
Tools Required:
• Phillips head screwdriver
• standard screwdrivers
• a 3/8 and 7/16 inch open end wrench
• set of marked drill bits
• an electrical multimeter tester capable of measuring continuity
• gas pressure gauge or manometer (gauge - AOS pt. no. 8099-2)
• water pressure gauge (AOS pt. no. 4798)
• thermometer (AOS pt no. 4870 - range 0 - 220 degree F)
• 1/2 inch socket with extension for removal of the clean out cover,
• 1 1/16 inch socket with extension for anode removal.

MISC: TC-043 Revision 1 vs. TC-043
Revision 1:
Adds Additional model’s information.
•
Adds cover statement this Handbook’s also a Service Handbook for many BTC Models.
•
Includes Power vent kit information.
•
Includes BTR/C-500 gas valve information.
•
Updated Damper illustrations.
•
Revision2:
Revised Part Numbers on Page 15
•
Revision 3:
Adds information unique to the Efflkal damper equipped (Series 110, 111 and
•
Retrofit) models

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INSTALLATION
This portion of the handbook will review some often overlooked installation
considerations, taking note of necessary installation requirements for the BTR 120
through 500 model heaters. The installation manual covers most of these items in detail.

CLEARANCES FROM COMBUSTIBLES

Clearance to Combustibles Table
MODEL
120 - 200
250 - 305
365 - 500

A
1” (2.54CM)
2” (5.08CM)
3” (7.75CM)

B
1” (2.54CM)
2” (5.08CM)
3” (7.75CM)

C
1” (2.54CM)
2” (5.08CM)
3” (7.75CM)

A 24 inch clearance for all serviceable parts is recommended. Clearances may vary
between BTR models – See instruction manual or the label on the heater, for clearances
applicable to your specific model.

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EXTERIOR CLEARANCE

"Copyright by the American Gas Association. Used by permission of the copyright holder".

This illustrates the exterior roof clearances for BTR units with natural draft venting. The
vent shall extend at least 3 feet above the highest point where it passes through a roof of
a building, and at least 2 feet higher than any portion of a building within a horizontal
distance of 10 feet (for vents of 12" in diameter or less). (NFPA 54 ANSI Z 223.1 SEC
7.5.2a). (Sec 7.6.2a may allow reduction to 8 feet with a “ Listed vent cap”).

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AIR FOR COMBUSTION
10 CUBIC FEET OF AIR PER 1,000 BTU

1 ,0 0 0
BTU

10 CU.
FT.
COMB.
AIR

2.5 CU.
FT.
EXCESS
AIR

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 1000 BTUH
input applies to natural and propane gas models.
The National Fuel Gas Code also specifies minimum make-up air opening sizes for
various building installations. (Ref: NFPA 54, ANSI Z223.1, sec 5.3)

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MAKE-UP AIR
DIRECT COMMUNICATION

1 Square
Inch Per
4,000
BTUH

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 twelve 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 downdraft condition occur. Additionally, when the heater is installed in a
confined space and communicating with the outdoor air, one permanent opening,
commencing within 12 in. (30 cm) of the top of the enclosure, shall be permitted where
the equipment has clearances of at least 1 in. (2.5 cm) from the sides and back and 6 in.
(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:
2
a. 1 sq. in. per 3000 BTU per hr (7 cm per kW) of the total input of all equipment
located in the enclosure, and
b. Not less than the sum of the areas of all vent connectors in the confined space.

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MAKE-UP AIR
VERTICAL DUCTS

1 Square
Inch Per
4,000
BTUH

Often it is more practical to install vertical make-up air ducts to the out doors. Again, two
openings are required - one within 12 inches of the top of the enclosure and one within
twelve 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.

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MAKE-UP AIR
HORIZONTAL DUCTS

1 Square
Inch Per
2,000
BTUH

Daily Schedule

When the heater is installed in an interior room with no roof access for vertical ducts,
horizontal make-up air ducts should be installed. When using horizontal ducts, two
openings are required - one within 12 inches of the top of the enclosure and one within
twelve inches of the bottom of the enclosure. 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.

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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 spillage, flame roll out, improper
combustion, inconsistent pilot operation, and/or erratic heater shut down.

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CONTAMINATED AIR

Along with adequate make-up air, the quality of the air is important. Contaminants in
combustion air can lead to premature heater failure. Vapors from bleaches, soaps,
waxes, salts, etc. are drawn into the combustion chamber with the make-up air and, once
fired, mix with water vapor in the gases to form extremely corrosive hydrochloric or
hydrofluoric acid and other corrosive byproducts.

AIR FOR COMBUSTION
Flammable Items

Flammable items, pressurized containers or any other potentially hazardous articles must
never be placed on or adjacent to the heater. Open containers of flammable material
should not be stored or used in the same room with the heater.

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GAS PRESSURE REQUIREMENTS

Supply Gas

Manifold
Pressure
Tap
Dirt Leg
Manifold
Gas Port

Maximum Supply Pressure

Natural Gas
13.8" w.c.

Propane Gas
13.8" w.c.

Minimum Supply Pressure

4.5" w.c.

11" w.c.

Manifold Pressure

3.5 " w.c.

10" w.c.

The supply gas pressure is normally measured at the dirt leg or at the gas pressure
tapping on the gas supply shutoff valve. This reading must be measured with 'flowing'
gas.
The manifold gas pressure is measured at the manifold pressure tap of the gas valve
when the gas is flowing.

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BTR GAS VALVE
The gas valves used on all BTR water heaters are
24 volt AC combination step opening gas valves.
They incorporate the pilot valve, main valve, and gas
pressure regulators into one body. The inlet view of
the valve features a filter screen and the top knob.
The top knob is a manual on/off gas control for both
the pilot and main gas valves. When the top knob is
placed on the black mark, gas is supplied only to the
pilot valve.

On the top view, we see the pilot solenoid and
pilot and main gas regulators. The top view also
displays the “TH and “TR” terminals. The pilot
gas regulator is found under its cover screw. It is
factory preset at 3.5”w.c. but can be adjusted from
2.5 to 5 inches water column. The main gas
regulator is found under its cover screw. It is
factory preset to 3.5 inches w.c. and adjusts gas
pressure output from 2.5 to 5 inches water
column. The two electrical terminals are marked
TH and TR. The TH terminal is the common
between the pilot valve solenoid coil and the main
valve solenoid coil. The other wire emerging from
the pilot solenoid connects to the pilot valve
electrical output on the IID (terminal PV). The TR
terminal connects directly to the main valve
electrical output from the IID module
(terminal MV).

On the outlet view of the gas valve, we see the
pilot gas connection port, manifold gas connection
port, a limited bleed vent port, the manifold gas and
pressure tap.
See step 18 for BTR-500 gas valve illustration

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VENTING
Atmospheric Multiple Heaters
Chimney

A minimum of ¼” rise
per foot of horizontal
vent is required.

All BTR water heaters are classified by ANSI as category I (non-condensing, negative
pressure venting) appliances. They are approved for type B vent.
For larger applications, BTR water heaters can be common vented together either in a
tapered manifold or constant size manifold. (Follow National Fuel Gas Code
requirements for sizing and installation.)
BTRs may be common vented only with other category I appliances. (See venting
section in the National Fuel Gas Code).

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DRAFT INDUCER

Draft inducers can be used with BTR water heaters to mechanically aid a lazy chimney in
vertical vent applications. They are not designed to allow “through-the-wall” vent
installations. (See Power Venter)

SINGLE UNIT INSTALLATION
When mechanically venting, the following items are required:
Qty
1
1
1
1

Description
Draft Inducer (up to 300,000Btuh)
Draft Inducer (up to 305,000 thru 500,000 Btuh)
Draft Prover Switch
Relay Switch

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Part No.
90909
90910
95220
96695

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POWER VENT KITS FOR SIDEWALL VENTING

Female plug
to Damper

40’, Power Venter
cable with “Y”
connect

Male plug
to Cable

Water Heater Models
BTR-120-200

Part Number
193933-0

BTR-250-500

193933-1

BTR water heaters can be used
with power vent kits for sidewall
venting. A.O. Smith offers power
vent kits for use on installations with
a maximum of 100 equivalent feet
of vent piping. The power vent kits
also use type B vent materials.
When power venting, specific
exterior clearances must be
maintained, as outlined in the
National Fuel Gas Code. (NFPA
54, ANSI A223.1, sec 7.8)

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BTR SEQUENCE OF OPERATION

9. Flue damper closes
2. Flue damper opens

1. Thermostat calls for heat
7. Thermostat satisfies

4. Pilot gas opens,
Pilot sparks and
flame proves
3. Intermittent
Ignition Control

6. Main burner ignites
5. Main gas valve opens
8. Main and pilot
burners "OFF"

SEQUENCE OF OPERATION
To understand BTR tank type water heaters, an examination of their sequence of
operation is necessary.
When the thermostat calls for heat, the relay in the draft hood assembly activates, deenergizing the flue damper motor. The damper opens and power flows to the IID
(Intermittent Ignition Device). This activates the IID module to open the pilot valve
and begin sparking at the pilot burner assembly. Once the pilot flame is established
and confirmed back to the IID, the sparking is stopped and the main gas valve is
opened, allowing gas flow to the main burner. When the thermostat satisfie’s, main
and pilot gas is shut off.

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BTR ELECTRICAL SEQUENCE
100 – 109 Series

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BTR ELECTRICAL SEQUENCE OF OPERATION
1 2 0 V ac to J u n c tion B ox

O n / O F F S witch "O N "

2 4 V Tran s form er

S eries 1 1 0 an d 1 1 1
E ffikal

Tan k Tem p eratu re

Tan k Tem p eratu re
S atisfied

H ig h L im it C los ed

H ig h L im it (E C O )
C los ed

Th erm ostat C losed

M otor C los es
D am p er

M otor R elay In terru p ts
P ower to M otor
M otor O p en s
D am p er

D am p er S p rin g O p en s
D am p er B lad e

C am O n D am p er B lad e
C los es P rovin g E n d S witc h

IID M od u le
(2 4 V ) R ec eives V oltag e

M od u le (P V ) Tem in al
S en d s 2 4 V to P ilot C oil

M od u le (S p ark ) S en d s
1 0 ,0 0 0 V S p ark to P ilot

P ilot Ig n ites an d P roves F lam e

S p ark S top s

M od u le (M V )
Term in al S en d s 2 4 V
To M ain G as C oil

9 0 S ec on d Trial /
5 M in u te D elay B etween
Trials - C on tin u ou sly

M ain B u rn er H eats Tan k

Th em ostat O p en s

S eries 1 1 0 an d 1 1 1
E ffikal

P ower to D am p er
R elay (4 ) In teru p ted

P ower to D am p er
# 2 In terru p ted

D am p er M otor E n erg ized
an d D am p er C los ed

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TROUBLESHOOTING BTR WATER HEATERS
To troubleshoot a BTR water heater check that:
•
•
•

120 VAC is supplied to the heater
the tank is full of water
gas is supplied to the unit

STEP 1

TEST THE TRANSFORMER

STEP 1 - TO TEST THE TRANSFORMER - Using a multimeter, test for 24 VAC
between the secondary transformer terminals.
IF
The meter does not read 24 VAC:

THEN
• Check that the 120 VAC is supplied
from the On/Off Switch – if not, replace
switch.
• Check that the 120 VAC is supplied
from transformer.
• Go to step 2.

The meter reads 24 VAC:

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STEP 2

HIGH LIMIT, LEFT TERMINAL TEST

STEP 2. HIGH LIMIT, LEFT TERMINAL TEST. Test for 24 VAC between the left high
limit terminal and ground.
IF
The meter does not read 24 VAC:

THEN
• Check wiring between transformer and
high limit.
• Go to Step 3.

The meter reads 24 VAC:

Note: The high limit (Energy Cut Off) opens if the tank water temperature exceeds 205
degrees. The control is resettable (manually) when the tank water temperature drops
below 185 degrees.
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STEP 3

TEST HIGH LIMIT RIGHT TERMINAL

STEP 3. TO TEST HIGH LIMIT RIGHT TERMINAL. Ensure that the jumper wire
between the high limit and thermostat is connected, and the damper motor power line is
connected. Test for 24 VAC between the high limit right terminal and ground.
IF
THEN
The meter does not read 24 VAC: • Push the reset button and redo the test (storage
water temperature below 185 degrees).
The meter reads 24 VAC:
• Go to step 4.
After Push in Reset - 24 VAC is now present

Condition
High limit open
Excessive water temperature
Heater shut down before
reaching thermostat setting

Reasons For Resetting
Cause
Never set on initial
installation
Faulty thermostat
Faulty high limit

Solution
Push high limit button
Replace dual control
Replace dual control

Note: The right terminal of the high limit has a jumper wire connected to the left terminal of the
thermostat. There is also a black wire connecting to the damper motor assembly. This black wire
supplies power to the motor to close the damper during periods of standby.
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STEP 4

INSPECT THE DAMPER

Effikal Damper Open
STEP 4. INSPECT THE DAMPER. Lower the thermostat setting so the unit will not be
calling for heat, then inspect the damper.
IF
If the damper is open:
If the damper is closed:

THEN
• Go to step 5.
• Go to step 7.

Note: If the water temperature in the tank is below 120 degrees F, temporarily disconnect the
jumper wire between the high limit and thermostat to simulate a satisfied thermostat.

STEP 5

CHECK THE PC BOARD

STEP 5. CHECK THE PC BOARD. Test for 24 VAC between the black PC board wire
connection and ground.
IF
24 VAC is not present:

THEN
• Check the black wire connections
between PC Board and high limit.
• Go to step 6.

24 VAC is present:
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STEP 6
Service Switch

PC BOARD MOTOR TEST
Motor Lead
Terminals

STEP 6. PC BOARD/MOTOR TEST. Check for 24 VAC between the two motor lead
terminals of the PC board. Disconnect the wires for this test.
IF
24 VAC is not present:

THEN
• Replace the board (AOS part # 6522)
and go to step 7. The board and relay
are one piece. Regardless of which
part is defective, both parts should be
changed.
•
This verifies that the motor is receiving
power but not closing the damper.
•
Replace the motor (AOS part # 6521)
and go to step 7.

Voltage is present:

Note: The service switch may be used to bypass the damper, while waiting for a replacement part.

WARNING - In the event of damper motor failure, verify that the damper is in the "open"
position before utilizing the service switch. (BTR Series 106/107 and some prior series –
changed from momentary push button to service switch).
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STEP 7

THERMOSTAT TEST

STEP 7. THERMOSTAT TEST. Set the thermostat to call for heat.
multimeter, test for 24 VAC between right terminal and ground.

Using your

IF
THEN
The meter does not read 24 VAC and the jumper wire • Replace the thermostat
between the high limit and the thermostat is in place:
The meter reads 24 VAC:
• Go to step 8.
Note: If the high limit to thermostat jumper wire was disconnected earlier to simulate a satisfied
thermostat, reconnect the jumper to the terminals.
Note: A yellow wire from this thermostat terminal connects to the damper PC board.

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GO TO PAGE 27 FOR DAMPER TESTS OF EFFIKAL EQUIPPED (SERIES 110, 111 AND
RETROFIT) MODELS

STEP 8

DAMPER INPUT TEST
Test from
Orange
wire to
Black
(neutral)

STEP 8. DAMPER INPUT TEST. Test for 24 VAC between the yellow wire on the PC
board and ground. Effikal – Check from orange wire to neutral
IF
24 VAC is not present:

THEN
• Check the black wire connections
between the PC board and high limit.
• Go to step 6.

24 VAC is present

STEP 9

TEST THE DAMPER

STEP 9. TEST THE DAMPER. Visually check the damper blade position.
IF
The damper does NOT open fully:
The damper DOES open fully:
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THEN
• Replace the damper assembly
• Go to step 10.

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STEP 10

TEST DAMPER OUTPUT

STEP 10. TEST DAMPER OUTPUT. On a call for heat, the damper relays receives
power through the yellow wire and power to the motor is interrupted. Then, the motor
clutch is disengaged and the damper opens. The damper proves it is open via an end
switch before power flows through the red wire from the PC board.
Place the red test probe on the solder joint of the red wire connection to the damper PC
board.
IF
THEN
The meter does not read 24 VAC and the • Replace the PC board
end switch is closed:
The meter reads 24 VAC
• Go to step 11.
Note: The spring rotates the damper blade assembly to the open position. This closes an end
switch.
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EFFIKAL DAMPER
BTR Series 110 and 111 began using the motor open; motor close, Effikal Damper. The
wiring colors from the damper PC Board are different from previous series BTR(C) and
BTC Models.

Service
Switch

Motor
Lead

Service
Switch

Adapter
Plug

Motor
Lead
Terminal

Heater
Harness

Effikal Control Cover (Photo of kit mounting)

Motor

Effikal Style

The heater harness wires still serve the same function:

Yellow

From Heater

Black

Damper
Black – 24V Constant if high limit closed
2
1
3
4
Yellow – 24V To damper if the thermostat is closed
Red – 24V From damper to IID if damper closes end switch
White – Neutral (common)
Orange Brown Yellow Black

White

Red

Male Plug

Female Plug

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HARNESS CHART
Heater Harness
Black
Yellow
Red
White

Function
24V Hot
24V from Therm
24V from damper
24V common

Damper Harness
1-Brown
2-Orange
3-Yellow
4-Black

Series 110 and 111 heaters and converted model BTR(C) and BTC heaters with Effikal

Dampers.

NORMAL OPERATION
Condition:
• Heater on standby
• Damper closed
• High Limit closed

Wires are from left to right:
Black i Yellow i Brown i White

STEP A

TEST FOR 24VAC BETWEEN BLACK (COMMON)
AND BROWN

STEP A. TEST FOR 24VAC BETWEEN BLACK (COMMON) AND BROWN
IF
24VAC is present
24VAC is not present

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THEN
Continue to Step B.
See Troubleshooting Step A1

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NORMAL OPERATION (continued)
Condition:
• Thermostat closed, damper in process of opening

STEP B

TEST FOR 24VAC BETWEEN BLACK AND ORANGE

IF
24VAC is present
24VAC is not present

THEN
Continue to Step C.
See Troubleshooting Step A2

Condition:
• Thermostat closed, damper fully open

STEP C

TEST FOR 24VAC BETWEEN BLACK AND YELLOW

IF
24VAC is present
24VAC is not present

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THEN
Continue to Step 11
See Troubleshooting Step A3

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TROUBLESHOOTING THE EFFIKAL STYLE DAMPER
Condition:
Thermostat closed, damper

Wires are from left to right:
Black i Yellow i Brown i White

STEP A1

TEST BETWEEN BLACK (COMMON) AND BROWN
ON THE DAMPER BOARD

IF
24VAC is present
24VAC is not present

THEN
This is correct
• See Steps 1 thru 4
Check the harness plugs connecting heater
and damper for looseness or damage.

Condition:
Thermostat closed, damper in process of opening.

STEP A2

TEST FOR 24VAC BETWEEN BLACK AND ORANGE

IF
24VAC is present
24VAC is not present

A.O. Smith Water Products
Irving, Texas ©2000

THEN
This is correct
• See Step 7
• Check the harness plug connecting
heater ----or damaged

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TROUBLESHOOTING THE EFFIKAL STYLE DAMPER (continued)
Condition:
Thermostat closed, damper is open fully

STEP A3

TEST FOR 24VAC BETWEEN BLACK AND YELLOW

IF
24VAC is present
24VAC is not present

A.O. Smith Water Products
Irving, Texas ©2000

THEN
This is correct – continue to Step 11
• See Step 9
• Check the harness plug connecting ---• Check that cam on shaft rotates with
shaft
• Replace the damper board

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STEP 11

WIRE HARNESS TEST

STEP 11. WIRE HARNESS TEST. Test for 24 VAC between terminal 24V on the IID
module, and 24V (GND).
IF
24 VAC is not present:
24 VAC is present:

THEN
• Check the wiring harness.
• Go to step 12.

Note: This test may be easier to conduct by removing the red wire from the IID terminal. Test for 24
VAC between the red wire and ground. Reconnect the red wire to the 24V terminal after the test.

A.O. Smith Water Products
Irving, Texas ©2000

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STEP 12

IID MODULE TEST

STEP 12. IID MODULE TEST (Power to the Pilot Valve). Using a multimeter, test for
24 VAC between terminal PV and 24V (GND) on the IID during the 90 second trial for
ignition.

IF
THEN
The meter does not read 24 VAC and the • Replace the module.
IID module is not between ignition trials:
The meter does read 24 VAC:
• Go to step 13

A.O. Smith Water Products
Irving, Texas ©2000

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STEP 13

PILOT SPARK TEST

STEP 13. PILOT SPARK TEST. Visually check for spark at the pilot assembly.
Note: The pilot burner mounts on the left side of the main burner.
IF
The igniter is not sparking:

THEN
Check for:
• A 7/64” spark gap
• Spark cable continuity
• Ground cable continuity
• Go to step 14.

Sparking is present:

Power To Module May Be Interrupted To Reset .

Call for
heat

90 sec.

5 min.

Sparking

No
Sparking

A.O. Smith Water Products
Irving, Texas ©2000

Trial for Ignition
90 sec.
5 min.
Sparking

No
Sparking

90 sec.
Sparking

Continuous
Trial
Sequence

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STEP 14A

PILOT VALVE - OHM TEST

BTR 120 – 400 GAS VALVE
STEP 14A. PILOT VALVE - OHM TEST. If pilot assembly is sparking but no pilot flame
is established, disconnect the pilot valve solenoid leads. Using a multimeter, (set to read
ohms) test for 20* ohms resistance +/- 5 through the solenoid coil.
IF
The meter dose not read 20 ohms plus or
minus 5:
The meter does read 20 ohms plus or
minus 5:

A.O. Smith Water Products
Irving, Texas ©2000

THEN
• Replace gas valve
•

Gas valve should work. Also check that
pilot gas is present and pilot tube or
orifice are not blocked

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STEP 14B

PILOT VALVE TEST – BTR 500 ONLY
PILOT GAS
MANIFOLD
PRESSURE
TAP

BLUE

WHITE
RED
The MV/PV wire on the IID is connected to the white wire

The MV wire on the IID is connected to the red wire.
MANIFOLD
GAS

MANIFOLD
PRESSURE
TAP

STEP 14B. PILOT VALVE TEST – BTR 500 ONLY. Testing the two coils of the
Honeywell VR8404P 5004 gas valve used on the model BTR 500 only. Because of built
in diodes, it is difficult to test for ohms resistance through these coils. The following is a
DC amperage check of the main and pilot coils.
Condition:
•
Tank calls for heat
•
PV terminal of module has 24 Vac
•
No Pilot flame
Test Procedure:
•
Turn off power to heater
•
Meter set to test for DC amperage (on AOS meters, the black wire is in the
“com” port, the red wire is in the “10A” port, the dial is set to 20M/10A in the DC
AMP test area).
•
Blue “PV” wire is disconnected from the ignition PV terminal.
•
Install meter in series between gas valve and ignition module – 10A wire to
blue gas valve lead, common wire to PV module terminal.
•
Turn power on to heater, after module receives 24V
Test DC Amperage through Pilot coil of gas valve
IF
THEN
.75 to .85 DCA is not present:
• Replace the gas valve
.75 to .85 DCA is present
• Pilot should work if gas (not air) is present to pilot
Power off, reattach blue gas valve wire to PV terminal of module.
A.O. Smith Water Products
Irving, Texas ©2000

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STEP 15

MAIN BURNER TEST

Note: BTR series 108 and 109 implemented a new main burner stamping process –
burners appear the same as illustrated.

STEP 15. MAIN BURNER TEST. Visually check for main burner.
IF
The main burner ignites:
The main burner does not ignite

A.O. Smith Water Products
Irving, Texas ©2000

THEN
• Sequence is complete
• Go to step 16

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STEP 16

FLAME RECTIFICATION

STEP 16. FLAME RECTIFICATION
Note: Flame rectification means that an alternating current (AC) signal is changed to a direct current (DC)
signal. The pilot flame is the 'switch' which connects the pilot hood to the igniter and ground. If the pilot
hood and igniter sensor had the same surface area, the flame 'switch' would conduct an AC signal.
Because the pilot surface is greater than the igniter surface, the signal becomes a DC current that the
module can interpret. The pilot hood must be properly grounded and the pilot flame must remain in
contact with both surfaces for the flame proving signal to remain constant.
If the signal is broken for just 8 tenths of a second, the heater will cycle off.
Sparking at the pilot will continue if an insufficient signal is received by the module.
Sparking at the pilot will stop almost immediately after the ignition module senses the pilot flame.

IF
Sparking continues after pilot is
established:

THEN
• Check wire connections
• Check flame contact between hood
and lighter
• Clean pilot burner surfaces
• Replace pilot assembly
• Go to step 17.

Sparking stops:
A.O. Smith Water Products
Irving, Texas ©2000

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STEP 17

IID MODULE TEST

Pilot is lit - Sparking has stopped.
STEP 17. IID MODULE TEST (Power to the Main Valve). Using a multimeter, test for
24 VAC between terminal MV on the IID and 24V (GND).
IF
24 VAC is not present:

THEN
• Replace the IID module. Conduct Step
18 before applying power to
replacement module.
• Go to step 18.

24 VAC is present:

A.O. Smith Water Products
Irving, Texas ©2000

Service Handbook
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SERVICE HANDBOOK

STEP 18A

MAIN GAS VALVE CHECK

TH
TR

BTR 120 – 400 GAS VALVE

STEP 18A. MAIN GAS VALVE CHECK. Disconnect wires from gas valve TH and TR
terminals. Using a multimeter, test for 68 ohms plus or minus 5 between TH and TR on
the main valve coil.
IF
The meter reads ‘O’ or infinity
The meter reads 68* ohms plus or minus 5

A.O. Smith Water Products
Irving, Texas ©2000

THEN
• Replace the gas valve
• The main burner will ignite

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STEP 18B

MAIN GAS VALVE COIL CHECK

PILOT GAS
MANIFOLD
PRESSURE
TAP
BLUE

WHITE

The PV wire is connected to the blue wire
RED

The MV/PV wire on the IID is connected to the white wire.
The MV wire is disconnected from the gas valve.

MANIFOLD
GAS

MANIFOLD
PRESSURE
TAP

STEP 18B. MAIN GAS VALVE COIL CHECK – BTR 500 ONLY
Condition:
•
Pilot lights
•
Sparking stops
•
No main burner ignition
Test Procedure:
•
Power off
•
Disconnect red, main valve wire from module MV terminal
•
Meter set to test for DC amperage
•
10A wire to red gas valve wire, COM wire to MV terminal of ignition module
•
Turn power on to heater
•
After pilot lights and sparking stops

IF:
.25 to .35 DC Amps is not present
.25 to .35DCA is present

THEN:
• Replace the gas valve
• Main burner gas should ignite.

Be certain to correct you meter wire connections and setting before performing further
tests.

A.O. Smith Water Products
Irving, Texas ©2000

Service Handbook
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BTR TANK TYPE HEATERS
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BTR WIRING DIAGRAM - NATURAL AND PROPANE GAS
Honeywell Ignition System (110 – 109 Series)

IF ANY OF THE ORIGINAL WIRE AS SUPPLIED MUST BE
REPLACED, USE ONLY TYPE 105° C THERMOPLASTIC OR
EQUIVALENT.

BLUE

WHITE MV/

RED

MV
GAS VALVE FOR
BTR-500/A ONLY

A.O. Smith Water Products
Irving, Texas ©2000

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GENERAL SERVICE CHART
CONDITION
DAMPER OPENS NO POWER
TO IID MODULE

PILOT LIGHTS, SPARKS
CONTINUOUSLY

CAUSE
. DAMPER NOT FULLY OPEN

SOLUTION
.EFFIKAL – REPLACE DAMPER CONTROL
ASSEMBLY
. REPLACE DAMPER

. DEFECTIVE PROTECTOR
SWITCH

. REPLACE PC BOARD

PILOT FLAME NOT PROVING

SEE FLAME RECTIFICATION - STEP 16
INTERRUPT 120 VAC POWER

HEATER WILL NOT IGNITE

NOT PROVING PILOT
FLAME EXISTANCE

. CHECK GROUND WIRE
ATTACHMENT
. CLEAN OR REPLACE PILOT
ASSEMBLY

PILOT GAS NOT COMPLETELY
INTERRUPTED AT END OF
HEATING CYCLE

. CHECK SUPPLY GAS PRESSURE
. REPLACE GAS VALVE

. THERMAL EXPANSION

ADD THERMAL EXPANSION TANK

. FAULTY VALVE

REPLACE RELIEF VALVE

LARGE VOLUME WATER
RELIEF FROM T&P VALVE

. EXCESSIVE WATER
TEMPERATURE
. FAULTY RELIEF VALVE

. CHECK WIRING
. REPLACE DUAL CONTROLLER
REPLACE RELIEF VALVE

PREMATURE TANK
LEAKAGE

CONDENSATION

. INCREASE STORED WATER
TEMPERATURE AND CONFIRM
PROPERLY SIZED APPLICATION

CONTAMINATED AIR

. REMOVE CONTAMINANTS.
. SUPPLY CLEAN COMBUSTION
AIR.
. ADD WATER HAMMER
ARRESTOR.
. REDUCE WATER PRESSURE.
. REMOVE UNNECESSARY CHECK
VALVES.
ADD THERMAL EXPANSION TANK.

WEEPING TEMPERATURE
AND
PRESSURE RELIEF VALVE

WATER HAMMER

THERMAL EXPANSION
DEPLETED ANODES

SCHEDULE ANODE CHECKS REPLACE AS NEEDED.

DAMPER WILL NOT OPEN

BINDING SHAFT
SHAFT SPRING WEAK/BROKEN
DAMPER MOTOR

NO SPARK AT PILOT DAMPER FULLY OPEN

DAMPER ASSEMBLY

SUPPORT VENTING
REPLACE DAMPER NON-EFFIKALS
REPLACE MOTOR EFFIKAL-REPLACE DAMPER
CONTROL ASSEMBLY
REPLACE PC BOARD - SEE STEP 10
Services Switch may bypass problem until
replacement part is received. (EFFIKAL –
REPLACE DAMPER CONTROL ASSEMBLY
REPLACE IID STEP 12
REPLACE CABLE STEP 13

IID MODULE
SPARK CABLE

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GENERAL QUESTIONS AND ANSWERS
Q.

What changes caused series 106/107 and 108/109 to be implemented?
A.
The 106 and 107 series units changed from the momentary push button to a slide
switch. The 108 and 109 series implemented a new main burner construction process. The
damper boards with service switch and new style main burners will automatically be
replacement parts for previous series heaters if parts are ordered.

What is unique about the Canadian – BTRC – models vs. U.S. BTR models?
A.
The Canadian models have different dimensions to meet Canadian code requirements.

How much electrical power is required for a BTR water heater?
A:
The BTR models draw approximately .7 Amps at 120VAC.

The units require "leg kits" to meet National Sanitation Foundation standards. What are the
part numbers for these kits?
A:
The BTR model heaters need AOS kit numbers:
BTR 120-400 (except BTR 197&198 series 100) = Part # 6570-0
BTR 197&198 Series 100 = Part # 6570-5
BTR 500 = Part # 6570-7

When should BTRs be delimed?
Many variables affect the liming up process including:
water temperature - The amount of lime accumulation during the same period of time will be
nearly 2 times greater if water is stored at 140 degrees F than at 120 degrees F. A 180
degree setting will build up lime about seven times as fast as a 140 degree F setting.
volume of water - The more gallons flowing through the BTR, the more rapid the
accumulation.
hardness – The harder the water the faster lime build up occurs. 1 to 3.5 grains per gallon is
"soft", 3.5 to 7 grains per gallon is "moderate", 7 to 10.5 grains per gallon is "hard" and 10.5 +
grains per gallon is "very hard". (An aspirin is about 5 grains. One grain is equal to 17.1 parts
per million.)
A:
Deliming should be done when a slight rumbling or popping sound is detected when the main
burners are on.

What effect will lime build-up have on the BTR water heater?
A:
One eighth inch of scale build-up may reduce efficiency as much as 22%; a 1/4 inch build-up,
as much as 38%.
A:
Less efficient heat transfer means more bottom head expansion/contraction stress and
premature leakage.
A:
Heavy build-up on the bottom head and bottom portion of the flue pipes leads to more heat
transfer at the top of the flues. This can lead to stacking or erratic thermostat operation.

Anode rods provide additional protection against corrosion. When should these be
replaced?
A:
When large gouges or pits appear in the anodes, replace them. It is recommended that
these be inspected every 6 months.

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BTR MODELS 197 AND 198
Series 100-101

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BTR MODELS 197 AND 198 (continued)
Series 100-101

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PARTS LIST for BTR Models 197 and 198 Series 100 & 101

Item

Parts Description

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

Bracket For Main Burner Orifice............... 098044(5)
Main Burner ............................................. 192322
Main Burner w/Pilot Bracket..................... 193873-0
Pilot Burner Natural ................................. 193314-0
Pilot Burner Propane ............................... 193314-1
Gasket ..................................................... 99036
Pressure Plate ......................................... 99037
Screws, Self Tapping............................... 69852
Control, Ignition Module ........................... 193325
Control, Dual w/ECO ............................... 192828
Drafthood................................................. 192957-4
Manifold................................................... 76244-2
Instruction Manual ................................... 193927
Main Burner Orifice Natural ..................... 76243-32
Main Burner Orifice Propane.................... 76243-49
Anode Rod............................................... 43817-38 (4)
T & P Relief Valve ................................... 99465-7
Transformer ............................................. 193444
Inlet Tube ................................................ 192626
Gas Valve Natural.................................... 192827-2
Gas Valve Propane.................................. 192827-3
Off/On Switch .......................................... 193243

BTR 197

BTR 198
098044(5)
192322
193873-0
193314-0
193314-1
99036
99037
69852
193325
192828
192957-4
76244-2
193927
76243-32
76243-49
43817-42 (4)
99465-7
193444
192626
192827-2
192827-3
193243

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BTR MODELS 120 through 500
Series 104-105

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BTR MODELS 120 through 500 (continued)
Series 104-111

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PARTS LIST FOR BTR Models 120 Through 500(A)
Series 104 Through 109 Series
(Series 106/107 have a service switch on Circuit Board 6522; Series 108/109 have new
main burner production method. Both parts will automatically be shipped
on 104 thru 109 series heaters.)
Item

Parts Description

BTR-120 BTR-154

BTR-180 BTR-199 BTR-200

1
2
3
4
5
6
7
8
9
10
11
11
12
13
14
15
16
17
18
19
20
21
22

Main Burner, Orifice Bracket
Main Burner
Main Burner w/Pilot Bracket
Pilot Burner, Natural
Pilot Burner, Propane
Gasket, Cleanout
Pressure Plate, Cleanout
Screw, Self tapping, Cleanout
Control, Ignition Module
Control, Dual w/eco
Drafthood
Drafthood 110, 111 Series
Manifold
Instruction Manual, (not illustrated)
Main Burner Orifice, Natural
Main Burner, Orifice, Propane
Anode Rod
T & P Relief Valve
Transformer
Inlet Tube
Gas Valve, Natural
Gas Valve, LP
Off/On Switch

98044(3)
192322
193873-0
193314-0
193314-1
99036
99037
69852
193325
192828
193597-0

98044(3)
98047
193873-1
193314-0
193314-1
99036
99037
69852
193325
192828
193597-1

98044(5)
192322
193873-0
193314-0
193314-1
99036
99037
69852
193325
192828
192957-0

98044(5)
192322
193873-0
R
193314-1
99036
99037
69852
193325
192828
192957-0

BTR-250
98044(5)
098047
193873-0
193314-4
193314-3
99036
99037
69852
193325
192828
193287

76244-0
193927
76243-32
76243-49
43817-38 (2)
99465-7
193444
193729
192827-2
192827-3
193243

76244-0
193927
76243-30
76243-46
43817-38 (2)
99465-7
193444
192626
192827-2
192827-3
193243

76244-2
193927
76243-35
76243-51
43817-38 (4)
99465-7
193444
193729
192827-2
192827-3
193243

76244-2
193927
76243-32
76243-49
43817-38 (4)
99465-7
193444
193729
192827-2
192827-3
193243

76244-2
193927
76243-32
76243-48
180618-42 (3)
99465-7
193444
192626
192827-2
192827-3
193243

76244-2
193927
76243-xx
76243-xx
180618-42 (4)
192467
193444
192626
192827-2
192827-3
193243

Item

Parts Description

BTR-251 BTR-275

BTR-305 BTR-365

BTR-400

1
2
3
4
5
6
7
8
9
10
11
11
12
13
14
15
16
17
18
19
20
21
22

98044(7)
98047
193873-0
193314-4
193314-3
99036
99037
69852
193325
192828
193287

98044(5)
98047
193873-1
193314-4
193314-3
99036
99037
69852
193325
192828
193287

98044(7)
192322
193873-0
193314-4
193314-3
99036
99037
69852
193325
192828
193287

98044(9)
192322
193873-0
193314-4
193314-3
99036
99037
69852
193325
192828
193287

BTR-500

76244-3
193927
76243-xx
76243-xx
43817-38 (4)
192467
193444
NA
192827-2
192827-3
193243

76244-2
193927
76243-xx
76243-xx
180618-42 (3)
192467
193444
192626
192827-2
192827-3
193243

76244-3
193927
76243-37
76243-48
43817-38 (4)
192467
193444
NA
192827-2
192827-3
193243

76244-4
193927
76243-32
76243-49
180618-42(4)
192467
193444
192626
192827-2
192827-3
193243

76244-4
76244-4
193927
193927
76243-31
76243-28
76243-48
76243-44
180618-42 (3) 180618-42 (4)
192467
192467
193444
193444
192626
192626
192827-2
193366-0
192827-3
193366-1
193243
193243

98044(9)
192322
193873-0
193314-4
193314-3
99036
99037
69852
193325
192828
193287

∗ For complete parts list call 1-800-433-2545

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COMPONENT PART INFORMATION
NAME
DUAL
CONTROLLER

THERMOSTAT

HIGH LIMIT
(ECO)
GAS VALVE

NATURAL GAS

PROPANE
GAS

INTERMITENT
IGNITION
DEVICE
CONTROL
DAMPER

SPECIFICATIONS

NATURAL GAS
AND
PROPANE
GAS
COMPLETE
ASSEMBLY
MOTOR

AOS # 192828

AOS # 192827-2

BTR 500; 24VAC, 60hz,
Dual Gas Valve,
STEP OPEN
BTR 120-400;
2.5 – 10” W.C.
STEP OPEN
BTR 500; 24VAC, 60hz,
Dual Gas Valve,
STEP OPEN

AOS # 193366-0

24 VAC, 50-60 HZ, .1A;
.7 MICROAMP SIGNAL
CONTINUOUS RETRIAL

AOS 193325

AOS # 192827-3

AOS # 193366-1

SEE PARTS LIST
24 VAC, 60 HZ, 120 RPM,
5 WATT

AOS #6521

Service Switch

AOS #6522

120 V PRIMARY, 24 VAC
SECONDARY,
40 VA, 50-60 HZ, CLASS 2
"B"

AOS #193444

P.C. BOARD
W/RELAY
TRANSFORMER

120-180 RANGE, + 4 , 5
DIFFERENTIAL,
LIQUID FILLED, ANTISTACKING
O
OPENS - 205 FIXED,
MANUAL
O
RESET BELOW 185
BTR 120-400;24VAC, 60hz,
.6A,.7” to 3.5” W.C.,
STEP OPEN

AOS PART NUMBERS

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BTR SERVICE CHECKLIST
(This service checklist may be photo copied to assist with BTR service call.)

This checklist is intended to aid the Service Agent in determining that the A.O. Smith
BTR Water Heater has been properly installed and is operating correctly. Because the
circumstances of each installation may vary greatly, it is not intended to be an allinclusive list of the problems that the Service Agent may encounter. Any item checked
"no" on this list should be thoroughly investigated and corrective action taken, if
required.
SERVICE AGENT
MODEL NUMBER
SERIAL NUMBER

INSTALLATION DATE
SERVICE DATE
LOCATION ADDRESS

GAS TYPE - CHECK ONE
PHONE(

NATURAL
PROPANE
I.

)

___ -

Check Clearances (circle answer)
A. Are exterior clearances adequate?
B. Are interior clearances adequate?

____

yes
yes

no
no

yes

yes
yes

no
no

yes

Comments:
II.

Check Makeup Air Requirements
A. Is the quantity of make-up air adequate per the National Fuel Gas Code?
Comments:
B. Is the quality of make-up air adequate?
Comments:

III.

Gas Pressure (fill in blank)
A.
Supply gas pressure
inches of w.c.
inches of w.c.
B.
Manifold gas pressure (main burner)
Comments:

IV.

Venting (check)
A.
Properly sized per the National Fuel Gas Code?
B.
Does the installation have mechanically assisted venting?
If so, is it operational?
Comments:

WATER PIPING

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VI.

Is the system properly sized?
Is the system properly installed?
Are there any water leaks?
Does the installation have a recirculating system?
If so, is it operational?

yes
yes
yes
yes
yes

no
no
no
no
no

PROPER SEQUENCE OF OPERATION
During standby does damper close on standby?
During standby is pilot flame off?
On a call for heat does thermostat close?
On a call for heat does damper open completely?
Does sparking begin at pilot?
Is pilot flame established?
If so, does sparking stop?
Does main burner ignite?
Does the thermostat satisfy?
Does damper close?

yes
yes
yes
yes
yes
yes
yes
yes
yes
yes

no
no
no
no
no
no
no
no
no
no

yes
yes
yes
yes
yes

no
no
no
no
no

no
yes
yes

no
no

Comments:
VII.

SAFETY
A. Gas
Does pilot flame prove before main burner ignites?
Does damper blade fully open before ignition sequence occurs?
Is burner cover plate in place?
Is burner floor shield in place?
Does IID lockout occur after 30 sec. trial for ignition? (Propane models only)
B. Water Temperature
Is the thermostat adjusted to the lowest acceptable temperature?
Does the installation have a mixing valve?
If so, is it operational?
What is the outlet temperature of the mixing valve?

yes

NOTE: (To minimize the risk of scalding, the manufacturer recommends storing water at 120°F.)
Is a properly rated temperature and pressure relief valve installed?

yes

C. Electrical
Is the 120 VAC electrical power supply properly wired?
Are all the BTR control covers in place?
Is the 120 VAC electrical power supply properly fused?

yes
yes
yes

no
no
no

D. Flammables
Are flammable materials located in the area of the water heater?
Are flammable vapors located in the area of the water heater?

yes
yes

no
no

Comments:
(This service checklist may be photo copied to assist with BTR service call.)

Service Handbook
1999 Training Department

BTR TANK TYPE HEATERS
SERVICE WORKBOOK

COMMENTS

Author: Terry Mulder

Service Handbook
1999 Training Department

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Author                          : TERRY MULDER

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A O Smith 120 Trough 500 Handbook NAME

120trough500 0c48242d-3c83-4152-90f5-c2442a241ec6 A.O. Smith Water Heater 120 trough 500 User Guide |

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