A.O. Smith BTX 100 How to use

1
PRINTED 0308 198142-000
COMMERCIAL / RESIDENTIAL GAS WATER HEATERS
FOR MODELS:
 • BTX-100
 • GDHE-50
SERVICEHANDBOOK
ULTRA HIGH EFFICIENCY
POWER VENT / POWER DIRECT VENT
http://waterheatertimer.org/power-vent-water-heater-troubleshoot.html
2008

ULTRA HIGH EFFICIENCY
POWER VENT/POWER DIRECT VENT
SERVICE MANUAL
Technical Literature Department ©2008
TABLE OF CONTENTS
INTRODUCTION ............................................................ 2
Qualifications............................................................ 2
Service Warning ....................................................... 2
Important Service Reminder..................................... 2
Instruction Manual .................................................... 3
Tools Required.......................................................... 3
INSTALLATION CONSIDERATIONS............................. 4
Closed Water Systems............................................. 4
Thermal Expansion................................................... 4
Air Requirements...................................................... 5
Contaminated Air...................................................... 5
Venting...................................................................... 6
Electrical Requirements............................................ 8
OPERATION & SERVICE............................................... 9
How it works............................................................. 9
Blower..................................................................... 10
Burner......................................................................11
Venturi .................................................................... 14
Gas Valve ............................................................... 15
Gas Pressure Testing............................................. 16
Air Pressure Switches ............................................ 18
Air Pressure Switch Operation ............................... 20
Air Pressure Switch Testing.................................... 21
Flame Sensing Test................................................ 24
Igniter Current Test................................................. 25
CONTROL SYSTEM..................................................... 26
Introduction............................................................. 26
UIM......................................................................... 27
Discreet Menu - Contact Information ............... 28
Operating Set Point Adjustment............................. 32
Control System Menus........................................... 33
CCB........................................................................ 35
Socket Identification......................................... 36
Wiring Diagram....................................................... 39
Sequence of Operation........................................... 40
TROUBLESHOOTING...................................................41
Rough Start - Rough Operation............13 and 41
Heater Status Menu..........................................33
Things to Check Before Servicing ....................41
Reset Procedure...............................................41
Control System Unresponsive.................................42
Blank Display....................................................42
UIM Inoperable.................................................42
Fault Messages.......................................................43
AC Reversed ....................................................43
Upper Probe Open............................................43
Upper Probe Short............................................44
Flame Probe Short............................................44
Flame Detect Error ...........................................45
Energy Cut Out (ECO)......................................45
Blocked Inlet.....................................................46
Blocked Exhaust Vent.......................................47
Blower Prover Failure.......................................47
Blower Prover Open - Blower Not Running ......48
Blower Prover Open - Blower Is Running.........48
Low Igniter Current...........................................49
Ignition Failure..................................................50
Gas Valve Failure .............................................52
Communication Failure.....................................52

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 2 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
INTRODUCTION
This Service Manual is designed to be an aid in servicing and troubleshooting the 96%
thermally efficient, 50 gallon, 100,000 Btu/hr residential and light duty commercial power
vent - power direct vent model water heaters listed on the cover of this manual.The
instructions, illustrations and procedures contained in this manual are used to verify proper
operation and to diagnose and repair common service problems.
This manual does not replace or supersede the Instruction Manual that came with the water
heater. Always refer to the Instruction Manual that came with the water heater for complete
installation instructions. If the Instruction Manual is not available copies can be obtained
from the manufacturers web site or by calling the technical support phone number shown on
the water heater labeling.
QUALIFICATIONS - QUALIFIED SERVICE AGENT
Servicing the products referenced in this manual requires the ability (in the field involved)
equivalent to that of a Qualified Service Agent as defined by the American National
Standards Institute (ANSI) below. Installation skills such as plumbing, air supply, venting,
gas supply, electrical supply are required in addition to diagnostic and electrical testing
skills.
ANSI Z223.1 2006 Sec. 3.3.83: “Qualified Agency” - “Any individual, firm, corporation or
company that either in person or through a representative is engaged in and is responsible
for (a) the installation, testing or replacement of gas piping or (b) the connection, installation,
testing, repair or servicing of appliances and equipment; that is experienced in such work;
that is familiar with all precautions required; and that has complied with all the requirements
of the authority having jurisdiction.”
SERVICE WARNING
If you are not qualified (as defined by ANSI above) and licensed or certified as required by
the authority having jurisdiction to perform a given task do not attempt to perform any of the
service or installation procedures described in this manual. If you do not understand the
instructions given in this manual or do not feel confident in your abilities to perform a given
task do not attempt to perform any procedures outlined in this manual.
IMPORTANT SERVICE REMINDER
When performing any troubleshooting step outlined in this Service Manual always consider
the wiring and connectors between components. Perform a close visual inspection of all
wiring and connectors to and from a given component before replacement. Ensure wires
were stripped before being crimped in a wire connector, ensure wires are crimped tightly in
their connectors, ensure connection pins in sockets and plugs are not damaged or worn,
ensure plugs and sockets are mating properly and providing good contact.
Failure to perform this critical step or failing to perform this step thoroughly often results in
needless down time, unnecessary parts replacement, and customer dissatisfaction.

Technical Literature Department 3 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
INSTRUCTION MANUAL
Have a copy of the Instruction Manual that came with the water heater on hand for the
correct model water heater you are working with before servicing.
Installation information given in this Service Manual is not a complete installation
instruction. Installation information covered in this Service Manual has a limited focus as it
applies to servicing. This Service Manual does not replace or supersede the Instruction
Manual that came with the water heater. Always refer to the Instruction Manual that came
with the water heater for complete installation instructions.
If the Instruction Manual is not on hand copies can be obtained from the manufacturers web
site or by calling the technical support phone number shown on the water heater labeling.
TOOLS REQUIRED
• Instruction Manual that came with the water heater.
• All tools common to installation and service of commercial water heaters such as hand
tools, torch, pipe wrenches etc.
• Long (8-10”) T handle SAE hex (allen key) wrenches including 5/32”, 1/8” and 1/4” - for
blower, burner, and gas valve removal and installation.
• Two digital manometers range -20.00 to +20.00" W.C., resolution - 0.01" W.C.
Recommend UEI model EM200 or equivalent. Required to test performance of air
pressure switches. Also used to measure low pressure supply gas and manifold gas
pressure.
• Digital Multi Meter DMM; recommend Fieldpiece HS36, Fluke 187, UEI DL289 or
equivalent capable of measuring:
• AC/DC Voltage
• AC Frequency (Hz)
•Ohms
• DC micro amps µA (flame sensing current)
• AC amp meter- recommend UEI model DL289 or equivalent.
• 120 VAC household outlet tester (see Service Notes Electrical page 8)

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 4 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
INSTRUCTION MANUAL
Installation information given in this Service Manual is not a complete installation
instruction. Installation information covered in this Service Manual has a limited focus as it
applies to servicing. This Service Manual does not replace or supersede the Instruction
Manual that came with the water heater. Always refer to the Instruction Manual that came
with the water heater for complete installation instructions.
If the instruction Manual that came with the water heater is not on hand copies can be
obtained from the manufacturers web site or by calling the technical support phone number
shown on the water heater labeling.
CLOSED WATER SYSTEMS
Water supply systems may, because of code requirements or such conditions as high line
pressure, among others, have installed devices such as pressure reducing valves, check
valves, and back flow preventers. Devices such as these cause the water system to be a
closed system.
Virtually all commercial and most residential water supply systems are closed systems
today. Closed water systems will experience thermal expansion which, if not controlled with
a properly installed and sized thermal expansion tank, can cause premature failure
(leakage) of the water heater. Water heater failure (leakage) on closed systems where there
is not a thermal expansion tank installed is not covered under the limited warranty.
THERMAL EXPANSION
As water is heated, it expands (thermal expansion). In a closed system the volume of water
will grow when it is heated. As the volume of water grows there will be a corresponding
increase in water pressure due to thermal expansion. Thermal expansion can cause
premature tank failure (leakage). This type of failure is not covered under the limited
warranty. Thermal expansion can also cause intermittent temperature-pressure relief valve
operation: water discharged from the valve due to excessive pressure build up. This
condition is not covered under the limited warranty. The temperature-pressure relief
valve is not intended for the constant relief of thermal expansion.
A properly sized thermal expansion tank should be installed on all closed systems to control
the harmful effects of thermal expansion.

Technical Literature Department 5 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
AIR REQUIREMENTS
Carefully review the requirements for combustion and ventilation air in the Instruction
Manual that came with the water heater. Failure to meet these requirements when the water
heater is installed or overlooking their importance when servicing the water heater often
results in needless down time, unnecessary parts replacement, and customer
dissatisfaction. If the Instruction Manual is not on hand copies can be obtained from the
manufacturers web site or by calling the technical support phone number shown on the
water heater labeling.
An inadequate supply of air for combustion and ventilation often causes operational
problems. A lack of combustion and ventilation air can create a negative ambient air
pressure in the installed space which can lead to improper combustion and operational
problems with air pressure switches.
CONTAMINATED AIR
Combustion air that is contaminated can greatly diminish the life span of the water heater
and water heater components such as hot surface igniters and burners. Propellants of
aerosol sprays, beauty shop supplies, water softener chemicals and chemicals used in dry
cleaning processes that are present in the combustion, ventilation or ambient air can cause
such damage.
Vapors from volatile compounds such as solvents, cleaners, chlorine based chemicals and
refrigerants in addition to being highly flammable in many cases, can also react to form
highly corrosive substances such as hydrochloric acid inside the water heater’s combustion
chamber. The results can be hazardous and cause product failure.
If this water heater will be installed in beauty shops, barber shops or laundries with dry
cleaning equipment, it is imperative the water heater be installed as a Direct Vent appliance
so that air for combustion is derived directly from the outside atmosphere through a sealed
intake air pipe. See the Installation of Vent System section in the Instruction Manual that
came with the water heater for more information on Direct Vent installations.

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 6 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
VENTING
The venting information presented in this Service Manual is not a complete venting
installation instruction. Refer to the Instruction Manual that came with the water heater for
complete installation instructions.
The water heater covered in this Service Manual may be installed as a conventionally
vented water heater or as a direct vent water heater. Conventional vent installations use
room air for combustion. There will be one “vent” pipe installed on a conventional vent
installation. Direct vent installations derive all air for combustion from the outdoor
atmosphere through a second “intake air” pipe. There will be two pipes (vent and intake air)
installed on a direct vent installation.
The vent and intake air piping (direct vent installations) may not be combined with any other
appliances under any conditions.
Maximum Equivalent Length Requirements
The vent and intake air pipe (direct vent installations) for the water heater covered in this
Service Manual can be installed using 2, 3, or 4 inch pipe depending on the overall
“equivalent” length of each pipe; see Table 1 on page 7.
The vent and intake air terminations do not factor into the overall equivalent feet
calculations.
The vent and intake air connection fittings on the water heater do not factor into the overall
equivalent feet calculations.
Additional 2 or 3 inch 90° elbows installed are equivalent to 5 linear feet of pipe. Additional 4
inch 90° elbows are equivalent to 8 linear feet of pipe. 45° elbows will count for half the
equivalent length a 90° elbow does.
Overall equivalent lengths are determined by adding the total length of pipe installed to the
accumulated total equivalent length of all the additional elbows factored in.
The maximum equivalent lengths given in the Instruction Manual that came with the water
heater and shown in Table 1 (page 7) are for the vent pipe AND for the intake air pipe. IE: A
2 inch vent pipe can be up to 20 equivalent feet with one 90° elbow. On a direct vent
installation the 2 inch intake air pipe can also be up to 20 equivalent feet with one 90° elbow.
Carefully review the venting installation instructions and maximum equivalent length
requirements for the vent and intake air piping. Ensure the vent system has been installed
per Instruction Manual requirements.
2”
3”
4”
= 5 linear feet of pipe
= 5 linear feet of pipe
= 8 linear feet of pipe

Technical Literature Department 7 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
VENTING (CONT)
Pipe Size Requirements
Ensure the correct size pipe has been used for the overall equivalent length of the vent and
intake air piping installed. Longer equivalent lengths require larger pipe sizes, see Table 1.
Maximum Elbow Requirements
Three and four inch vent and intake air pipe installations allow a maximum of 6 - 90° elbows
in the vent pipe AND a maximum 6 - 90°elbows in the intake air pipe. Two inch installations
allow a maximum of 3 - 90° elbows in the vent pipe AND a maximum 3 - 90° elbows the
intake air pipe.
Table 1
Service Notes - Venting
Remove all plastic debris from the edges of intake air pipe sections after cutting on direct
vent installations. Plastic debris left on intake air pipe sections can collect inside and clog the
burner and lead to rough operation and/or ignition failure. See Service Notes page 11.
Using a smaller pipe size than required for a given length or installing more elbows on the
vent pipe can cause the water heater’s control system to declare a fault condition, lock out
and display the “Blocked Exhaust” fault message on the UIM display (see page 27).
Overlooking the same requirements for the intake air pipe on direct vent installations or
failing to remove the screen from the intake air connection when direct venting can cause
the water heater’s control system to declare a fault condition, lock out and display the
“Blocked Inlet” fault message on the UIM display (see page 27).
NUMBER
90° ELBOWS
2” MAXIMUM PIPE
LENGTH FEET (METERS)
3” MAXIMUM PIPE
LENGTH FEET (METERS)
4” MAXIMUM PIPE
LENGTH FEET (METERS)
1 20 (6.1) 60 (18.3) 120 (36.6)
2 15 (4.6) 55 (16.8) 112 (34.1)
3 10 (3.0) 50 (15.2) 104 (31.7)
44 elbows not allowed in 2” pipe
(use larger pipe size) 45 (13.7) 96 (29.3)
55 elbows not allowed in 2” pipe
(use larger pipe size) 40 (12.2) 88 (26.8)
66 elbows not allowed in 2” pipe
(use larger pipe size) 35 (10.7) 80 (24.3)
The screen inside the intake air connection is meant to keep
larger debris from entering the blower when the water heater is
installed conventionally; using room air for combustion.
When the water heater is installed in a direct vent configuration
the screen inside the intake air connection on the water heater
must be removed. If left in place it will become clogged over time
and lead to “Blocked Inlet” lock out conditions.
The screen on the intake air termination will keep larger debris
from entering the blower on direct vent installations.
Remove This Screen
For Direct Vent
Installations

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 8 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ELECTRICAL REQUIREMENTS
The water heater covered by this Service Manual must be grounded in accordance with
the local codes, or in the absence of local codes: the National Electrical Code (NFPA 70) or
the Canadian Electrical Code (C22.1).
The water heater covered by this Service Manual requires a 120 VAC 1Ø (single phase)
power supply. It is factory equipped with a standard 3 prong appliance cord that plugs into a
standard 120 VAC wall outlet. 5.2 FLA (full load amps) approximate.
As shown in the illustration below there should be 120 VAC present between the power
supply hot and ground wires. 120 VAC should also present between the hot and neutral
wires. There should be 0 VAC present between the neutral and ground wires.
Correct wiring for a standard 120 VAC wall outlet is also shown in the Illustration below. Note
the orientation of the ground connect is at the bottom. Reversed polarity is when the hot and
neutral wires are connected opposite from what is shown here.
Service Notes - Electrical
This water heater is a polarity sensitive appliance and will not operate if the power supply
polarity is reversed. If the polarity of the power supply is reversed the water heater’s control
system will declare a fault condition and display “AC Reversed” on the UIM display.
The water heater’s burner must be grounded for flame sensing current to be established and
verify ignition. If the burner is not grounded the water heater’s control system will declare a
fault condition and display “Ignition Failure” on the UIM display after 3 failed ignition trials.
Also shown is an outlet tester that will quickly determine if the plug is wired correctly. These
testers will also diagnose reversed polarity, open ground and open neutral wire problems.
Outlet testers are inexpensive and simple to use. They are available at most hardware
stores and home centers.
120 volts
120 volts
0 volts
HOT NEUTRAL GROUND
HotNeutral
Ground
120 VAC 1Ø
Wall Outlet
Correctly Wired Outlet120 VAC 1Ø Power Supply
Outlet Tester

Technical Literature Department 9 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
OPERATION & SERVICE
HOW IT WORKS
This section of the Service Manual will cover operation, common service procedures and
water heater construction. The water heater covered in this Service Manual has a helical coil
shaped heat exchanger that is submerged in the storage tank. The water heater uses a top
mounted down fired radial burner. This is a forced draft burner; hot burning gases are forced
through the heat exchanger under pressure and exit through the exhaust/vent connection
located at the bottom of the water heater.
COMBUSTION
AIR INTAKE
CONNECTION
EXHAUST/VENT
CONNECTION
INTERNAL VIEW
EXTERNAL VIEW
Starting at the top combustion air and
fuel gas are drawn in by the blower
(page 10) and Venturi (page 14).
The hot burning gases exit the radial
burner (page 11) and are forced
through the coil shaped heat
exchanger.
Flue gases spiral through the heat
exchanger and exit the water heater
through the exhaust/vent connection
at the bottom.
HELICAL
SHAPED
HEAT EXHNGER
BLOWER/BURNER
GAS VALVE
ASSEMBLY
COMBUSTION
AIR INTAKE
CONNECTION
EXHAUST/VENT
CONNECTION