Bosch 125HX NG User Manual

INSTALLATION AND OPERATING INSTRUCTIONS FOR AUTOMATIC
INSTANTANEOUS TYPE WATER HEATERS FOR USE WITH NATURAL AND
LIQUEFIED PETROLEUM GAS

MODEL 125HX LP and 125HX NG

(Flow Modulated with Electronic Ignition)

Suitable for heating potable water only

Not approved for space heating purposes

Intended for variable flow applications with steady cold water inlet temperatures.

WARNING

If the information in this manual is not followed
exactly , a fire or explosion may result causing property
damage, personal injury or death.

FOR YOUR SAFETY

Do not store or use gasoline or other flammable,
combustible or corrosive vapors and liquids in the
vicinity of this or any other appliance.

WHAT TO DO IF YOU SMELL GAS

- Do not try to light any appliance.

- Do not touch any electrical switch; do not use any

phone in your building.

- Immediately call your gas supplier from a neighbor’s

phone. Follow the gas supplier’s instructions.

- If you cannot reach your gas supplier, call the fire

department.

- Installation and service must be performed by a

qualified installer , service agency or the gas supplier.

WARNING: Improper installation,

adjustment, alteration, service or maintenance can
cause injury or property damage. Refer to this manual.
For assistance or additional information consult a
qualified installer , service agency or the gas supplier.

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Upon completion of the installation, these instructions
should be handed to the user of the appliance for
future reference.
In the Commonwealth of Massachusetts this product
must be installed by a licensed plumber.

FEA TURING: Automatic V ariable Power Modulating Gas
V alve and power generated Electronic Ignition

T ABLE OF CONTENTS

Specifications .................................................... Page 2

Rules for safe operation .................................... Page 4

Locating the Heater ............................................ Page 4

Combustion Air Requirements ............................ Page 5

Mounting the Heater........................................... Page 5

Venting the Heater ............................................. Page 6

Gas Connections ............................................... Page 7

Gas Piping ......................................................... Page 8

Water Connections ............................................ Page 9

Safety before turning on the heater..................... Page 9

Operating instructions ...................................... Page 10

Setting water temperature ................................ Page 10

Maintenance & Service......................................Page 1 1

Trouble Shooting ...............................................Page 1 1

Electrical Diagram............................................ Page 13

Diagram of AquaS tar......................................... Page 15

Interior components diagram ............................ Page 16

Parts List ......................................................... Page 17

Principle of Operation:

When a hot water faucet is opened, the water flow through
the heater causes the gas valve to open. At the same
time the hydro-generator activates the electronics which
sends a spark to the pilot. The flame sensor confirms the
pilot has been lighted and allows the first two burners to
come on. The flame sensor confirms correct activation and
all burners come on. The pilot goes off. The heat exchanger
coils absorb the heat generated by the burners and transfer
heat to the water. When the hot water faucet is shut of f, the
gas valve automatically closes and the burners turn off.
Y our hot water faucet is an ignition key to activate the water
heater, giving you control over your hot water energy use.
Every time you turn off your hot water faucet, the energy
consumption of your hot water returns to zero.

AquaStar 125HX LP and 125HX NG Specifications

Gas Input max.: 117,000 Btu/hr

min.: 28,000 Btu/hr

Water Connection ½” Thread fitting NPT

H x W x D 29 3/4” x 18 1/4” x 8 3/4"
Vent 5”
CA TEGORY I GAS APPLIANCE
Gas Connection 1/2” NPT thread

FEATURES

- Electronic Pilot Ignition driven by hydro-generator

- High Quality Materials for Long Working Life.

- Copper heating coils for endless supply of hot water.

- Burner output proportional to hot water flow demand for
maximum energy efficiency .

- Safety flame sensor at pilot burner.

- Automatic overheating protection shut-off sensor .

- Flue gas safety device.

- St ainless steel burners with stabilized blue flame.

- Built-in corrosion resistant draft diverter .

- Compact space saver: mounts on a wall with two hooks.

- Easily removable one-piece cover.

- Easy one person installation.

- Adjustable water flow restrictor to ensure that water flow
demand will not exceed the heating capacity of the
heater.

- On/Off Switch to activate system.

Min. Water Pressure 18 Psi at 4 GPM
Max. Water Pressure 150 Psi
Shipping Weight 43 LB
Net Weight 40 LB

1.8 GPM at 90° rise

3.7 GPM at 45° rise
Min. Water Flow 1/2 gal/min
LP GAS Supply Pressure

(before Aquastar regulator) min. 1 1” W.C.

max. 14” W.C.*

Required LP GAS Pressure at inlet
tap while Aquast ar is operating: 10.5” W.C.

LP GAS Burner Manifold pressure while Aquastar is
operating at maximum input: 9.0” W.C.

Natural Gas Supply Pressure min.: 7” W.C.
(before Aquastar regulator) max.: 14” W.C.*

Required Natural Gas Pressure at inlet
tap while Aquast ar is operating: 5.7” W.C.

- Red LED indicator flashes with low water pressure.

- Green LED indicator main burner operation.

BOSCH is constantly improving our products, therefore
specifications are subject to change without prior notice.

Natural Gas Burner Manifold Pressure while Aquastar is
operating at maximum input: 4.2” W.C.

* Inlet gas pressure before Aquastar regulator must not
exceed this value. Pressure may need to be adjusted for
high altitudes, see page 7.

UNPACKING THE AQUASTAR HEATER

This heater is packed securely . The box includes one water connection fitting, a control knob, a gas pressure regulator ,
a pressure relief valve, an incandescent particle tray , two hooks for hanging the heater , this manual, a personal letter , a
warranty statement and a warranty registration card. Do not lose this manual, as there is a charge for replacement.
Please complete and return the enclosed warranty registration card.

2 6 720 606 804 (02.10)

FRONT VIEW SIDE VIEW

MINIMUM INST ALLATION CLEARANCES FROM COMBUSTIBLE AND NON
COMBUSTIBLE MATERIALS FOR ALCOVE OR CLOSET INSTALLATIONS

MODEL 125 HX

TOP (A) 12"
FRONT (B) 4"
BACK 0"
SIDES 4"
FLOOR (C) 12" *
VENT DIAMETER 5"

* Some local codes require 18” in garage installations

AQUASTAR MODEL 125HX

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GENERAL RULES TO FOLLOW
FOR SAFE OPERATION

1. You should follow these instructions when you install

your heater. In the United States: The installation must
conform with local codes or, in the absence of local codes,
the National Fuel Gas Code ANSI Z223.1/NFP A 54.
In Canada: The Installation should conform with CGA
B149.(1,2) INST ALLATION CODES and /or local installation
codes.

2. Carefully plan where you install the heater. Correct

combustion air supply and flue pipe installation are very
important. If not installed correctly, fatal accidents can be
caused by lack of air, carbon monoxide poisoning or fire.

3. The place where you install the heater must have enough

ventilation. The National Fire Codes do not allow gas fired
water heater installation in bathrooms, bedrooms or any
occupied rooms normally kept closed. See the section below
on locating the heater.

4. You must vent your heater . See section on VENTING,

Page 6.

5. The appliance must be disconnected from the gas supply

piping system during any pressure testing at pressures in
excess of 1/2 Psig (3.5 kPa).
The appliance must be isolated from the gas supply piping
system by closing its individual manual shutoff valve during
any pressure testing of the gas supply piping system at
test pressures equal to or more than 1/2 Psig (3.5Kpa).
The appliance and its gas connection must be leak tested
before placing the appliance in operation.

6. Keep water heater area clear and free from combustibles

and flammable liquids. Do not locate the heater over any
material which might burn.

7. Correct gas pressure is critical for the optimum

operation of this heater (see specifications on page 2). Gas
piping must be sized to provide the required pressure at
the maximum output of the heater, while all the other gas
appliances are in operation. Check with your local gas
supplier, and see the section on connecting the gas supply .

The heater may still operate even when improperly vented.
It will, however, be less ef ficient and could eventually damage
the heater. It could even result in human sickness or death
due to oxygen deprivation and carbon monoxide poisoning.
Follow the guidelines below:

1. Place your heater as close to a vent or chimney as
possible.

2. National building codes require that you do not install
this appliance in bathrooms, bedrooms or any occupied
rooms normally kept closed.

3. Simultaneous operation of other appliances such as
exhaust fans, ventilation systems clothes dryers, fireplaces
or wood stoves could create a vacuum effect in your home
which could cause dangerous combustion by-products to
spill back into your home rather than venting to the outside
through the flue. Confirm that your Aquastar is venting
properly when all these other appliances are running. See
section on venting.

Do not obstruct the flow of combustion and ventilation
air to the appliance. If installed near a clothes dryer it is

very important that the dryer be properly vented. Failure to
properly vent a dryer could result in a gradual accumulation
of lint on the water heater fin coils and burners, leading to a
dangerous condition of vent blockage and poor unsafe
combustion.

4. Y our hot water lines should be kept short to save energy .
It is always best to have hot water lines insulated.

WARNING: The water in this water heater is cold

and always remains cold except for the times that hot
water is being used DO NOT INSTALL IN AN AREA

WHERE IT COULD FREEZE.
This heater is neither designed for nor approved for
outside installation.
Drain the heater entirely if freezing temperatures are
anticipated in area where heater is installed by
disconnecting both the inlet and outlet water
connections from the heater (disconnect the outlet flex
line from where it connects to the copper heat
exchanger). Additionally remove the drain plug under
the water valve. See Fig. 0.

8. Should overheating occur or the gas supply fail to shut

off, turn off the gas supply at the manual gas shut off valve
on the gas line.

9. Do not use this appliance if any part has been

underwater. Immediately call a qualified service technician
to inspect the appliance and to replace any part of the
control system and any gas control which has been
underwater.

Fig. 0 - Water heater drain plug

PROPER LOCATION FOR INSTALLING
YOUR HEATER

Carefully select the location of your new heater. For your
safety and for proper heater operation, you must provide an
abundant supply of combustion air and a proper venting.

4 6 720 606 804 (02.10)

WARNING: Flammable materials, gasoline,

pressurized containers, or any other items or articles
that are potentially fire hazards must NOT be placed
on or adjacent to the heater. The appliance area must
be kept free of all combustible materials, gasoline
and other flammable vapors and liquids.

This product is not approved for manufactured homes
(mobile home), recreational vehicles (RV) or boats.
Reference ANSI Z21.10.3.
This product is neither designed or approved for

outside installations.

COMBUSTION AIR REQUIREMENTS

The AquaStar water heater holds cold water in its copper
heat exchanger and water valve when not in use. Because
of this, any cold air that comes in through the unit’s vent
pipe is capable of freezing these components. This
Installation Manual specifies the minimum vertical vent pipe
and the amount of combustion air required for this unit.
The vent pipe must not be restricted and its 6 foot minimum
height (provided there are no elbows) must terminate 2 feet
above any obstruction within a 10 foot radius.
When all requirements are followed, the unit will operate
properly and safely. However, there may still be a risk of
freezing due to negative draft if all the combustion appliances
in the area are not being supplied with a sufficient amount
of make-up air. A wood stove or furnace can rob the make­up air in the AquaS tar’s vent pipe, leaving the cold infiltrating
air capable of freezing the cold water in the AquaS tar heat
exchanger. More make up air is the solution. Follow the
instructions on venting and checking adequacy of make up
air. A HVAC specialist should be used to design solutions
for providing more make-up air if necessary.

Observe the following instructions concerning combustion
air.

Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater

than 50 cubic feet per 1000 Btu per hour of the combined
rating of all appliances installed in the space.That would
be 5850 cubic feet for the AquaS tar 125HX alone.

b) In unconfined spaces in buildings of conventional frame,

masonry, or metal construction, infiltration is normally
adequate to provide air for combustion, ventilation, and
dilution of flue gasses.

Appliances located in confined spaces:
The confined space must be provided with two permanent
openings, one commencing within 12 inches of the top and
one commencing within 12 inches of the bottom of the
enclosure. Each opening must have a minimum free area
of one square inch per:

- 1000 Btu/hr if all air is taken from inside the building.

- 2000 Btu/hr if all air is taken from the outside by horizontal
ducts.

- 4000 Btu/hr if all air is taken from the outside by direct
openings or vertical ducts.

Or the confined space must be provided with one permanent
opening or duct that is within 12 inches of the ceiling of the
enclosure. This opening must have a minimum free area of
one square inch per:

- 3000 Btu/hr if all air is taken from the outside by a direct

opening or vertical duct.

Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of your
openings by 75% if your louvers are wood and by 30% if
your louvers are metal. Refer to the National Fuel Gas Code
for complete information. In buildings of tight construction

all air should be taken from outside.

CLEARANCES

The Aquastar 125 HX is design certified for inst allation on a
combustible wall and for installation in an alcove or closet
with the minimum clearances to combustible and non ­combustible construction listed below

A. Top 12 inches (306 mm)
B. Front 4 inches (102 mm)
C. Back 0 inches
D. Sides 4 inch (102mm)

E. Bottom 12 inches (306 mm)
Clearance from vent is dependent upon the clearance rating
of the venting material used. For example: type B-1 vent is
approved for 1 inch clearance.

Note: Minimum clearance to combustible materials should
not be less than 6" for single wall flue pipe. Note that this
clearance can be reduced if combustible material are
protected as per table VI of the National fuel Gas Code or if
Type B gas vent is used.

MOUNTING INST ALLATION

The Aquastar 125 HX is design certified for mounting on a
wall.
Secure the two L shaped hooks provided with the heater to
a wall surface. Place them 13 ¼ inches apart as shown in
Fig 1.
Do not install this appliance on a carpeted wall or over floor
covering which is combustible, such as carpet. The heater
must be mounted on a wall using appropriate anchoring
materials. If wall is a stud wall sheathed with plasterboard,

it is recommended that support board(s), either 1x4’s
or 1/2" (minimum) plywood first be attached across a
pair of studs and then the heater should be attached
to the support boards. See Fig 1.

Expansion and contraction of piping due to changing water
temperature in the pipes imparts movement to the heater
which, if mounted directly to a brittle, friable board, such
as plasterboard, can cause failure of mounting.
In earthquake-prone zones, CEC recommends that
installers use a large washer and lag screw through the
existing holes used to hang the heater to affix the upper
third of the heater to the mounting board. T o affix the lower
third of the heater, CEC recommends that two new holes
be drilled in the heater’s frame, each one 16 inches below
the top two holes, and that washers and lag screws be
used to secure the lower portion of the heater to a spacing
board.

Before installing the unit, be certain you have the
correct heater for your type of Gas – Propane or Natural
Gas. Identification labels are found on the shipping
box, and on the rating plate which is located on the
right side panel of the cover. Also, each burner orifice is

stamped with a number (79 for LPG and 120 for Natural
Gas).

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at least 1/4 inch for every foot of its horizontal length. Keep
the horizontal section short and avoid too many elbows.

WALL STUDS

13 ¼”

SUPPORT BOARD

1” X 4”

SPACE BOARD

Fig. 1 - Mounting the Heater

The incandescent particle tray (shipped loose in the carton
with the water heater) must be attached at the bottom of
the water heater front cover at the time of installation. Use
the screws provided. See figure 2

SCREWS

INCANDESCENT PARTICLE TRAY

Fig. 2 - Incandescent Particle Tray Illustration

VENTING

Vent pipe connection. W ARNING: Do not reduce

the vent pipe size.

This appliance must be vented to the outside following all
local ordinances and specifications for installing a gas
appliance vent or chimney. The venting system must be
designed and constructed so as to develop a positive flow
adequate to remove flue gasses to the outdoors. Minimum

vent size must be 5". Minimum vent height must be 6
feet, provided there are no elbows. Termination of
the vent must be 2 feet above any obstruction within
a 10 foot radius of the vent pipe. Consult your gas
utility or National Gas Fuel Code if vent will have
elbows or share venting with another appliance. The
vent connector should have as much vertical rise as
possible (minimum 12”) before any horizontal run.

Optional powervent (Model AQ-1) is available in order to
sidewall vent. In the Commonwealth of Massachusetts:

Powervented applications must utilize proof-of-draft
safety interlock device. Contact your local dealer. The

appliance must be located as close as practicable to a
chimney or vent. The vent pipe sections must be secured
to each other with sheet metal screws. Keep in mind the
minimum clearance from the top of your heater . Remember
also that single wall vent pipe connectors require a 6 inch
clearance from combustibles. National Fuel Gas Code
specifies double wall — T ype “B” — vent pipe be used in
cold climates and for gas vents running through attics. We
consider double wall vent pipe preferable in all
circumstances. Any vent section greater than 45 degrees
from vertical is considered horizontal.
Horizontal sections of vent connectors must slope upwards

T o check the draf t:

Close all doors and windows to the outside.
Turn on all appliances that force air out of the building.
These include all exhaust/ventilation fans, furnaces, clothes
dryers, wood burning stoves, etc.
Open all doors between the AquaStar and these other
appliances.
With the control knob set fully clockwise and strong hot
water flow rate, run the unit for at least 10 minutes. The
125HX is equipped with a Flue Gas Sensor; it’s mounted
on the right side of the draft diverter (Flue Gas Sensor #34
on page 17). If the main burners shut off during this test it
is because the Flue Gas Sensor has detected inadequate
venting. This is a serious health hazard and must be
corrected. Poor venting can result in soot building up inside
the heater, overheating of the heater and freezing of the
heat exchanger in a freezing environment, which is all a
result of negative air flow. Additional combustion air and/or
improved venting will be necessary to correct this.

WARNING

Note: The burners of an instantaneous “on demand” water

heater such as the AquaStar are only on at the time that
hot water is actually being used, the vent pipe is therefore
cold except for the short durations when hot water is being
used, it is therefore very important that the venting and air
supply be adequate to provide a good positive draft as
soon as the burners turn on. See venting guide on back
page.
The AquaS tar 125HX instantaneous water heaters have built­in draft diverters and are designed for indoor installation
only. The draft diverter outlet must be connected to a clear ,
unobstructed vent of the same size, or larger.

In Canada, CAN/CGA-B149 Installation Code for detailed
requirements
In U.S.A., ANSI Z223.1 - NFPA 54, National Fuel Gas
Code for detailed requirements.

The vent connection for the AquaStar 125HX is 5 inches.
However, in CANADA, for installations at high altitude (2000-
4500 feet above sea level) a six inch vent is required. A 5"
by 6" vent adaptor must be affixed to the vent collar of the
AquaStar with at least two screws. See figure 3.

WARNING: Failure TO INCREASE THE VENT SIZE

TO SIX INCHES AND/or assure that the manifold pressure
is set to proper value listed for applications at high altitudes
will cause unsafe venting, asphyxiation, and will void CSA
Certification.

5” X 6” ADAPT OR

USED ON HIGH AL TITUDE

Fig. 3 - Vent Adaptor for High Altitude Canadian

Installations

6 6 720 606 804 (02.10)